Nothing sums up fashion's current penchant for practicality better than the vogue for denim. Harriet Walker rediscovers the fabric for our distressed times

The autumn shows are great for trend voyeurism – from What's Big Right Now, to the Next Big Thing, to Something Else Big Lurking Just Around The Corner. Usually these "bigs" fall into esoterically different camps: think back to last season, when you had to decide between looking like Jethro Tull, the Queen or a robot. This time round, whether due to fiscal restrictions or consumerist ennui (unlikely), the fashionable set plumped unanimously for denim.

The humble workwear cloth was omnipresent, in every imaginable incarnation, from jeans to jackets, and in all conceivable styles, from retro street-cool to uptown bourgeois to avant-garde chic. The only decision you need to make is which tribe you belong to.

Denim has a reputation as an equaliser, a leveller of men. Originally made in France, serge "de Nîmes" was used for army fatigues, and the port of Genoa gave its name to traditional serge trousers: jeans. Also known as "hickory cloth", it was worn by American pioneers and later dustbowl cowboys. Perhaps this is why we find ourselves in tougher times looking towards this emblem of sturdiness and capability. That said, "equaliser" isn't quite the word to describe the £1,000 Balmain jeans, which just sold out at Net-A-Porter. Nor the "it" jeans of the season, by London label Meadham Kirchhoff, a £1,390 pair that has been meticulously bleached and slashed then artfully riveted and laced back together. Never mind – there's a practical whiff about fashion at the moment, and the vogue for denim just about sums it up.

The most "now" variety has to be stonewash – even acid wash – denim. Eighties in flavour but made modern by styling, oversized denim shirts were worn with skinny trousers at Alexander Wang; Riccardo Tisci showed boxy stonewash jackets with leather inserts at Givenchy. Make sure your look isn't too Back to the Future: nubile hipsters may look great in a fringed, snow-wash jacket, but it's an irony too far on most of us. Pale denim looks fresh and uplifting with black and white, so try a jacket or shirt with black leggings, or your jeans with an oversized T-shirt. Distressed and ripped is also a hot trend: small holes in the weft here and there look good on a classic blue straight-leg or baggier cut; full-on ripping and slashing works on skinny jeans in any hue (not forgetting black and grey). Wear with long tops or cropped jackets. The paler or more slashed the denim, the skinnier the fit should be; otherwise you risk looking like a Nineties student.

One other pitfall of denim is the bizarre urge it creates in the wearer to don multiple pieces. A full-length jumpsuit (try Asos) isn't out of the question, but separates are a different matter. Never mix shades of blue, only black or white if you must. And don't make the mistake Britney once did and pick out some hybrid creation that looks as if it was made from several off-cuts of denim tarpaulin. Do not proceed to style this up with a denim boyfriend (that's you, JT). And don't even think the words "denim accessories and a matching Stetson".

Generally though, it's easy to stay on the straight and narrow. Quite literally, in fact. Skinnies are the jeans that defined an era: previously that of Sid Vicious, but more recently of Kate Moss, Pete Doherty and Nicole Ritchie and her little matchstick legs. These styles are still around, but times have changed. The Hawley Arms has burnt down, and being a size zero during a recession when people really are going hungry is downright tasteless. Enter the cut of jeans to come: the skinny flare, tight on the thigh then wide to the foot. That's right, ladies – when times get hard, it's back to bootcuts. "Flares are very slimming and can make short girls look taller," says Donna Ida, eponymous owner of the London jeans emporium. "Make sure the knee is nicely nipped-in, and any bootcut will look instantly current. Try with a blazer: roll up the sleeves and wear with a classic white vest." Another shape that has come to the fore is the "boyfriend" jean, a baggy, masculine cut that sits low on the hip and is perfect for the weekend. "They're really just track pants by another name," Ida says. "Start wearing them now with booties or heels, then with flip-flops in the summer, and don't take them off till late October. It's the credit crunch jean!" Some of the best are by the new brand Current/Elliott.

The Acne for Lanvin collaboration includes jeans in this season's ultra-desirable shape – bagged out at the hips with a slightly tapered leg. Bridget Cosgrove, fashion and buying director at Matches, says: "Trouser shapes have taken their inspiration from the YSL carrot legs; J Brand's 'Steve' jean is also a good example."

Denim hotpants are also in the middle of a resurgence, but if the thought of busting out your Daisy Dukes literally leaves you cold, then layer a pair over leggings or opaque tights. And if none of these seem avant-garde enough, then you could always wear your jeans backwards à la Kris Kross.