A late contender for most relatable tweet of the year arrived in November courtesy of comedy writer Molly McNearney, who declared: “There’s never been a more confusing time for women to buy jeans.”

It’s hard to argue with her assertion. While most Gen Zs wouldn’t be caught dead in anything except wide-leg or flared jeans, older fashionistas are still struggling to come to terms with the demise of their beloved skinnies, and everyone else is somewhere in between.

Ultimately, each person must decide for themselves which hem and cut to adopt, but when it comes to jeans fit, some rules remain the same no matter what trend is in vogue at any given time.

Just ask Sali Hughes, journalist and author of Everything Is Washable (currently reduced to £21.99 from £26, Waterstones), a denim devotee who, after years of trial and error, has got jeans shopping down to a fine art.

Here, in an extract from the book, Hughes offers her expert advice on how to find your perfect pair…

Try on lots of pairs

“I generally avoid the horror of the changing room if I can possibly help it,” says Hughes, but she’s willing to make an exception when it comes to jeans.

“If you’re unsure of size, and on which style might best flatter, it’s worth biting the bullet and visiting a store – horrible fluorescent lighting and all.”

And don’t be afraid to ask for help from the sales assistants, who really know their stuff: “They will have seen every bum shape and leg length and will know exactly which jeans look best on whom.”

Get the rise right

So much focus is put on jean hems, but you really want to start by deciding on the length of the ‘rise’ – the length between the waistband and the crotch seam.

“By and large, a high rise will hit you at the narrowest part of the waist and give a smoother, more flattering shape to your abdomen,” says Hughes, “and also gives the illusion of longer legs – high-waisted jeans with flat shoes make me look taller than mid-rise jeans and high heels.”

Unlike hem length, a rise cannot be altered or tailored later, which is why it’s important to get it spot on.

“Those with very short torsos and long legs to spare may wish to drop to a midrise,” Hughes continues. “Few women – even those with the most banging bodies – look their best in a low rise. Who wants jeans that don’t allow for period bloat or a long, boozy lunch?”

The long and short of it

Want the illusion of longer legs? Don’t automatically discount cropped jeans.

“It’s a myth that cropped trousers make legs look shorter,” says Hughes, who is 5ft 3. “In fact, a flash of ankle usually makes short legs seem longer, and works for most footwear choices, either shoe or boot.”

She advises against hems that fall below ankle level, unless you’re very tall: “The exception to this rule is flares, which should mostly cover the shoe to not look weird.”

True colours

“In theory, the darker the colour, the smarter the jean. The paler the denim, the more casual,” says Hughes, who tends to favour indigo and mid-blue jeans.

“Dark navy rinse is elegant, slimming and can look dressy enough for even corporate wear,” she continues, as can black denim. “But bear in mind that a true black usually comes up smaller and you’ll need to size up one.”

Classic black denim (meaning fabric that is, in reality, dark grey) is “a good way to break up an all-black outfit, adding a little dimension and tone, and really very stylish.”

A bit of stretch

Fashion purists would have you believe jeans can only be made of 100% cotton denim, but if you prefer a bit of stretch in the fabric, go for it.

“I’ve concluded that 95-97% cotton denim jeans, i.e. ‘medium stretch’, are the most flattering,” says Hughes. “Much less cotton than that and the denim can cling visibly to your cellulite and bag over time in the knees and bum. Any more than 97% and you have yourself a rigid denim and you’ll probably need to go up a size.”

Confused by clothing labels? With denim you can forget about the breakdown of elastane, polyester or nylon, Hughes says: “Tencel and other fibres are frequently in the mix… just check the cotton count on the label and ignore the rest.”

A snug fit

One final thing to bear in mind when shopping for jeans is how to denim will adapt when worn.

“The right-sized jeans feel half a size too small when new,” says Hughes. “They’re not painful – they will do up with relative ease and you won’t have to hold your breath. But they will feel a tiny bit more snug than you will want them, and than they will soon be.”

The cotton count will make a difference, however: “Stretch denim will usually ‘give’ about half a size within a wearing. A rigid denim (like classic Levi 501s) may take a couple of wearings.”

And loose styles will get even baggier: “Jeans that feel perfectly relaxed and comfy upon purchase will quickly feel too big, which is fine if you’re buying loose boyfriend styles or pairs you plan to cinch in with a belt, but not ideal otherwise.”

Everything Is Washable And Other Life Lessons by Sali Hughes is published by Harper Collins, priced at £26.