From fruit-patterned swimwear to cactus-covered greeting cards and inflatable lobsters, it’s impossible to escape the zing of feelgood Americana. So why has everything gone totally tropical?

At Primark, the £6 best-selling bikini of the season has pineapples on it. If it has sold out in your size, though, don’t worry: online shop Asos has three different bikinis with pineapples on them. It has got phone cases, necklaces, backpacks and dressing gowns to match, too. At John Lewis, one in five products sold in the summer party department has a flamingo on it, as does every other birthday card in Paperchase. Ditto the fairy lights in the US clothing chain Anthropologie, and the USB sticks in Urban Outfitters. The vases in the window at Zara Home are shaped like cacti, as are the ones at The Conran Shop. At Oliver Bonas, you can find watermelon-slice earrings to match the watermelon beach ball you picked up at Selfridges, which goes so well with your new Dolce & Gabbana watermelon-painted handbag.

Describe a 1950s Palm Springs poolside cocktail party using only emojis, and you capture the aesthetic of summer 2017. The colours are pink and green (a flamingo with a palm tree, a watermelon slice). The shapes – pineapple, cactus, Martini glass – are as sunnily evocative and as easy to draw as a smiley face. Move over industrial chic bare bricks and copper pendant lights, because we are living in the Age of the Pineapple.

This skirt is not to be worn as you would on holiday, over a swimsuit. Treat it, instead, as you would a pencil skirt

The way to do summer-in-the-city dressing is to bring enough sunshine into your wardrobe to remind you that it’s summer out there, without looking as if you’ve come to work dressed as the sunglasses-wearing smiley face emoji. You want to change the mood in the way that opening a window and letting the breeze in changes the air in a room. This can happen in lots of ways: a rolled shirt sleeve, a bare ankle. You don’t have to wear spaghetti straps for your clothes to speak summer. You can wear white (read: Wimbledon) or yellow (sunshine) or gingham (picnics).

The sarong-wrap skirt is this summer’s crossover hit. Crossover, in this case, from summer holiday to summer-but-not-holiday. No one actually wears sarongs on holiday any more (how the kaftan killed the sarong will have to be a long read for another day), but the shape is still recognisable as beach-flavoured.

Related: What I wore this week: an asymmetric neckline | Jess Cartner-Morley

For the first time ever, Princess Diana is cool. Diana has been many things – the fairytale bride, the ill-treated wife, the pioneer of revenge dressing and, finally, the queen of hearts – but hip is the one thing she has never been. At her wedding in 1981, and again at her funeral in 1997, she was a tabloid goddess. In between, she was a Vogue cover star. But she was never an avant-garde muse – until now.

Virgil Abloh made his name as Kanye West’s creative director, and his Off-White label is now one of the hottest in the fashion industry. A profile in W magazine called him the “king of social media superinfluencers” and “a canny translator of youth culture”. His show in Florence last month was an installation combining fashion and poetry created in collaboration with the American artist Jenny Holzer; a political statement that Abloh described as being about “immigration and the plight of refugees”. Abloh has art-directed an album for Jay-Z and designed limited-edition sneakers for Nike.

More practical, less eccentric: a hippy classic gets a makeover

Freshly minted for summer 2017, I give you the non-eccentric kaftan. After half a century of alternative living, the kaftan has gone conventional. Where a kaftan once demanded a rooftop and soft drugs, the new look is perfectly at home on a sunlounger with a Diet Coke.

I am not sure I completely approve. I kind of liked the kaftan in its original format. I loved the free-spiritedness, the definitive out-of-office symbolism of joyously anti-power dressing. On the other hand, the new kaftan is a whole lot easier to wear.

Related: What I wore this week: a Birkin bag

The fashion magazines have released their Autumn bumper editions, essential for the style-conscious. Think rhinestones, Basquiat – and being ‘excited AF’ for autumn

Clothes that sit away from the body look grander, more elegant, more all-round fabulous than skintight ones

On the meta-issue of how to wear clothes in 2017, there is one essential piece of fashion advice which I am borderline evangelical about. Sometimes I have to restrain myself from running after women in the street and wrestling them to the ground in order to drum it into their heads. It is this: that loose clothes now look smarter and more modern than tight clothes. There is still a hard-to-shake-off mindset which tells us that loose clothes are casual – pyjamas, tracksuit bottoms – and that smartening up means tight skirts and fitted jackets. That making an effort means wrangling with Spanx and fastening your belt on its tightest notch. And it’s just not the case. Clothes that sit away from the body look grander, more considered, more elegant, more all-round fabulous than skintight ones.

Many women seem to feel that wearing clothes that do not trace the outlines of their body will somehow place them at a disadvantage. And if your gameplan is simply to maximise eyeballs on you, then sausage skin dressing is undoubtedly effective. But we can do better than that with our clothes, I think. Quality rather than quantity of audience engagement. And I have a proposal for you sceptics, if wearing a fluid, sack-shaped dress to a meeting sounds more alarming than wearing nothing at all. August is the ideal time to experiment, because this is silly season, and that applies to your wardrobe too. You don’t have to power dress. This is the ideal moment to loosen up.

Related: What I wore this week: the new kaftan

Rather than fighting online retail, bricks-and-mortar stores are try to bring shopping to life – and H&M’s new brand is leading the way with a Nordic cafe and a haberdashery department

Walk through the door of Arket, the hotly anticipated fashion-and-lifestyle brand that opens its first store on Regent Street in London this Friday, and the first thing that strikes you is the generous expanse of empty space. The tables are laid with individual items, rather than stacked with teetering piles. (Further available colours are stacked unobtrusively in cubes, labelled by size.) The flecked floor resembles cobbles or gravel, while the cabinets and paintwork are in a soft cloud-grey that makes the building feel almost invisible from within. The effect is more like wandering through an open-air market than a fast-fashion hothouse.

Arket calls itself “a modern-day market”. This is not a reference only to the mix of clothes and homeware, of decorative and functional (department stores have been doing that for centuries), but also to the spirit of market shopping. No longer demoralised by the rise of online retail, the high street is on a mission to bring back the joys of the shopping trip.

Fret not, not all of your holiday wardrobe has to sit unused in your wardrobe until your next trip. A lot can be said for a long hemline, even miles away from the beach – just be sure not to take floor-length too literally

There are some things that you have to leave behind when your holiday ends. Lunchtime rosé. Reading a book as a legitimate daytime activity. I’ll stop there before we both get weepy.

On a happier note, bits of your holiday wardrobe can transition back into real life. The bikinis, the pool sliders, the denim cut-offs, and anything with colourful pompoms hanging off it: those all have to go. Your trad sundress with the spaghetti straps, fitted bodice and full skirt isn’t realistically going to see the light of day for a while. There is, however, a chance of a reprieve for the maxi dress.

Related: What I wore this week: loose clothing

Fashion has a thing for female empowerment right now, which has moved on from feminist slogan T-shirts to office tailoring

A woman in a trouser suit shouldn’t be a contentious sight. However, as Hillary Clinton discovered, this is not the case: a woman in a trouser suit is a look that still invites comment. Whether it’s a politician making a speech in a bright-coloured pantsuit, a Helmut Newton model in a Parisian street wearing an Yves Saint Laurent Le Smoking tux, or a policewoman in uniform – a woman in a trouser suit is always seen as a challenge.

This autumn will be full of challenges, because trouser suits for women are happening in a major way. Fashion has a thing for female empowerment right now, which has moved on from feminist slogan T-shirts to expressing itself in corner-office tailoring. We don’t have time here to debate whether a trouser suit is intrinsically more empowering than a floral dress. All I’m going to say on the subject is that fashion means well by its talk of empowerment – even if it amounts to a hill of beans – and I don’t see how wearing trouser suits can do any harm, so long as we acknowledge that the Céline catwalk probably isn’t going to smash the patriarchy all by itself.

Related: What I wore this week: the new kaftan

Fashion’s embrace of cosy clothes for watching box sets is over. This season, designers are centring on a sharpened-up look – power dressing that empowers

The fashionable position to take on fashion, these days, is that trends are dead and that individual style and self-expression are what matters. The old certainties – skirts are hereby decreed knee length for six months, only camel coats are to be worn for the foreseeable – belong to a different era. To a bygone world in which political insiders gave ballpark-accurate election predictions and the Oscar statuette didn’t get handed to the wrong film in front of a global TV audience. Now the world is sick of experts, and that goes for fashion too.

Except in September. Because right now, the world needs fashion. The September issues of magazines, heavy as hymn books and immortalised by a glossy documentary, are testament to the power fashion has at this moment. Women who rely on their own style to steer their wardrobes the rest of the year are, at this point in the calendar as at no other, keen to be told which coat to buy and when to start wearing black tights. The system in which one consistent look could preside over a whole autumn and winter has been blown apart by an insatiable appetite for newness that demands we hit wardrobe-refresh every three weeks. September’s back-to-school moment, when you pack away the sundresses and straw baskets and revamp your look, is the one fixed red-letter-day that remains.

It is too early to say whether LVMH and Kering’s ban on using size zero models will improve women’s health, but it is a sign the business is changing

The use of size zero models has been a fashion industry scandal for 15 years. The announcement that rival Paris powerhouses LVMH and Kering have joined forces to end the practice is proof of an industry finally being held to account by the clothes-buying public.

Will their charter succeed in improving model health, after previous initiatives failed? It is too early to say. But the move is encouraging evidence of how fashion is being gradually democratised.

Related: French fashion giants pledge to stop using underage and size zero models

Ladylike or masculine, navy is the most modern of colours

Navy is a flattering colour to wear. Not in the complexion-enhancing sense so much as in the more significant all-round-vibe-enhancing sense. It won’t make your cheeks look peachy or your eyes piercing, it will emphasise your sparkling mind and innate class. Think of it like Touche Éclat for your personality instead of your under-eye shadows.

The magic happens because wearing navy makes you look like the sort of person who wears navy, and that is in itself a good look. Simple as that. The sort of person who wears navy has more gravitas than the person who wears, say, pink, but she doesn’t take herself quite as seriously as the person who wears black. She is as chic as the person who wears grey, but a little more grounded. She has just the right amount of French-girl allure: the messy-haired sexy bit, without the calculated coquettishness.

Related: What I wore this week: the maxi dress | Jess Cartner-Morley

Shayne Oliver, of Hood by Air, kicks off a series of guest takes on the designer whose look has never gone away

It is 12 years since the designer left the Manhattan fashion scene in favour of life as a sculptor in upstate New York, but the Helmut Lang look never went away.

Lang gave the modern urban creative class its uniform: snake-hipped, flat-fronted black trousers with a tissue-thin white cotton T-shirt; a slip dress with biker boots; a bomber jacket with paint-spattered jeans – all of these are classic Lang looks. They never went out of fashion, they just had a different name on the label.

Related: Fenty x Puma by Rihanna: ethnically diverse and exuberant

The designer invited just 300 guests to his New York fashion week show which was a celebration of affluence and exclusivity

The late 19th-century arbiter of Manhattan society Samuel Ward McAllister coined the phrase “The Four Hundred” to describe the number of people who really matter in New York at any given time. Ralph Lauren, who has built a personal fortune of $5.8bn (£4.4bn) by distilling the top notes of affluent east coast society into blazers, polo shirts and perfumes, revived this concept on Tuesday evening with an ultra-exclusive runway show, bucking the inclusive, consumer-facing direction that has defined most of New York fashion week.

In contrast to Alexander Wang’s Saturday night event, staged guerilla-style on downtown streets, Ralph Lauren selected just 300 guests to be chauffeur-driven out of the city for one glamorous evening, staging a runway show and black-tie dinner upstate among a personal collection of valuable vintage sports cars.

Hemlines are down, necklines up – and there are complicated politics behind fashion’s embrace of a looser silhouette

• Read more from the autumn/winter 2017 edition of The Fashion, our biannual fashion supplement

Do you prefer midiskirts that cover your knees to minis these days? When you wear a slip dress, do you sometimes layer a polo neck underneath it? On a lunchtime browse, do you find yourself drawn to a voluminous sleeve? If you are reading this, then the answer is probably yes. The look of 2017 is notably more demure than that of a decade ago. Hemlines have dipped a crucial few inches, from just above the knee to just below it. A collar up to your chin is the norm. Party dresses have sweeping sleeves, rather than plunging necklines. Or, to put it another way: for the simple reason that you are engaged with fashion, you have become a modest dresser.

When Victoria Beckham launched her fashion house a decade ago, her style had already left the Wag days behind. Cleavage and Daisy Dukes had been replaced by neat knee-length dresses whose necklines exposed only the clavicles. Since then her wardrobe – one of the most photographed and most influential in the world – has evolved further. Her clothes are now loose and fluid, concealing the shape as well as the surface of the body.

The designer’s New York show was a journey through the archives with headwraps and bold colour leading the way

That rumours of the artistic demise of the New York fashion week legend Marc Jacobs had been vastly exaggerated was evident when Anna Wintour broke into a run on Park Avenue to make sure she arrived on time for the start of Jacobs’ show. Even the US Vogue editor-in-chief, peerless in her power over the city’s fashion scene, could not afford to miss this.

Last month, Jacobs addressed persistent rumours that his label was in financial difficulties, telling Women’s Wear Daily there was no truth in gossip that he was set to hand over creative control, and adding that the talk was “upsetting and stressful” to his staff.

The singer has cemented her status with an epic show at New York fashion week and the launch of her own beauty brand

Announcing Rihanna as a keynote speaker at its prestigious fashion industry conference next month, Women’s Wear Daily described her as a “powerhouse multihyphenate”. This is perhaps the least clumsy way to describe what Rihanna does. As a singer, songwriter, actor, fashion designer, and – since the launch a week ago of Fenty Beauty – business mogul, the strings to Rihanna’s bow have become unwieldy to list. Luckily, she is too famous to need a job title.

Even by global megastar standards, Rihanna has had quite a week. As creative director of the sportswear company Puma, she staged an epic New York fashion week show, complete with motocross stunts across pink glitter mountains that delighted her fans and charmed the critics. The Washington Post said: “Rihanna has figured out how to sprinkle just the right amount of her stardust on the sportswear brand without overshadowing the brand itself.

A new season calls for a new jacket

A double-breasted blazer was the first thing I bought for this new season. Heretically, I don’t adhere to the industry edicts about snapping up coats at the end of July. My back-to-school moment happens at New York fashion week in early September, which is invariably roasting hot and yet wall-to-wall with women showing off their new outerwear. This season it was oversized teddy-bear, faux-fur coats in lipstick red. Which are divine, and I absolutely want one – but not yet. Some showgoers manage to pull them off – perhaps if you are truly, glacially ultra-cool you can lower your own body temperature – but for me they are out of the question until it’s actually cold enough. Being comfortable in your clothes is sometimes framed as the polar opposite of chic – the elasticated waistband, let-yourself-go look – but to me, it works the other way around. Great clothes are the ones that make your day feel easier and lighter, not the ones that are a burden.

Not that I am pretending to be immune to that late-August hunger for Something New. Far from it. This season, I absolutely had to have a double-breasted blazer the moment I got back from holiday. A lightweight jacket is the most direct way to ring seasonal changes, because it shapes the most visible part of your silhouette as well as fitting the climate. The jacket had to be a blazer, because I suspect that this autumn I am mostly going to be wearing longish, loose skirts and fluid trousers, and a blazer is the most elegant complement to that.

Related: What I wore this week: loose clothing

International stars have been lured by the city’s pop culture heritage, but fashion week is keeping its idiosyncratic edge

Fashion week is now in the entertainment business. Designers of today crave fans, not customers. London – home of the Abbey Road zebra crossing, of 221B Baker Street and of platform 9 3/4 at King’s Cross station – has world-class heritage as a city where pop culture history gets made. This blockbuster reputation has lured more big beasts of the industry to London than ever before. Giorgio Armani and Tommy Hilfiger are joining Donatella Versace on the catwalk schedule, and Rihanna will visit to showcase her Fenty Beauty line.

Hilfiger, the ultimate stars-and-stripes American designer – his logo even resembles the flag – has previously shown in New York and Los Angeles. This season, his show at the Roundhouse in Camden will serve as the closing party for London fashion week. “London has the most inspiring heritage as a city, and the Roundhouse itself is part of rock’n’roll history,” Hilfiger explains over the phone while preparing to travel to London. The venue has hosted legendary gigs including Jimi Hendrix in 1967 (his Fender Stratocaster was stolen from the side of the stage) and the Ramones in 1976. “The catwalk is just another kind of stage. Fashion has to go beyond clothes and be an experience. This is me taking the brand on the road for a world tour.”

Adwoa Aboah is both the poster girl for modern fashion and one of its most vocal critics. The 25-year-old model, who walked the Burberry catwalk on Saturday and Donatella Versace’s Versus show on Sunday, leads discussions around issues from imagery of black women in the media to the impact of social media’s hyperphotogenic visual culture on self esteem on Gurls Talk, the online platform she founded which now has 100,000 Instagram followers.

At London fashion week, real talk is the new air-kissing. The rise of Aboah, recently named a contributing editor at Edward Enninful’s British Vogue and GQ’s Woman of the Year, symbolises an unexpected taste for candour which is emerging in an industry long built on the pursuit of unattainable perfection.

Related: British Vogue: what we can expect from Edward Enninful as editor

Related: Model Adwoa Aboah: 'In 2017, there is more than one way to be beautiful ​and cool'