Carola Long: 'Black leather dress to a conservative christening? Hey, why not?'

With la rentree and a new batch of trends comes the biannual hope of radical reinvention. A new fashion horizon unfolds, and all that stands between one's tired old wardrobe and French Vogue-ishness is dropping a few hundred quid on a jacket with massive shoulders, something leather, perhaps some textured knits.

It was just such optimism, and possibly naivety, that led me to buy a grey suede dress from Cos, convinced that this garment (as sexy as leather but infinitely softer and less obvious) would provide the one statement piece around which the rest of my wardrobe will orbit. I looked in the changing room mirrors, and a vaguely Angelina Jolie-ish vision looked back, sort of. It was love.

And then doubt set in. Perhaps said dress was more Wilma Flintstone than Balmain. Perhaps the grey suede was a touch elephantine. I bought it anyway, but haven't worn it yet. And then I got to thinking, how can you tell whether your new season's dress is a statement piece, or (as my boyfriend "hilariously" put it) just a bank-statement piece, otherwise known as an expensive mistake. Herewith, some critical signs that you should leave a new trend in the shop:

If you are too embarrassed to come into the communal area of the changing room, you probably won't feel that hot wearing it in public. If you haven't worn it within a week of buying it, perhaps you never will. This still applies even if it's too warm for summer or a supposedly suitable occasion hasn't presented itself. When you are smitten with a new item you'll find a way to wear it. Black leather dress to a conservative christening? Hey, why not? If buying something necessitates purchasing more than one other piece to go with it or losing weight, you are inclined to lie about the cost or it has already been worn by Dannii Minogue; avoid like the plague - or rather, the swine flu.

More specific to this season, here are a few pointers when it comes to assessing whether you are "owning" the key trends or they are "owning" you. Naturally, we come first to big shoulders; if you are quite broad, either avoid them or go for a more crisp, angular shape with height, rather than wide or voluminous styles to avert the Honey Monster look. When it comes to Eighties patterned dresses, there is a fine line between the upscale Balenciaga effect and Pat Butcher. The key is in the fabric. Cheap material and Eighties shapes and colours do not mix. Considering some textured or crazy patterned knits? Ask yourself do I look at all, and I mean at all, like the geeky kid in About A Boy or his veggie mum (below)?

Of course trusting your instincts should be the best way to shop, and in an ideal world one would reject such checklists as anathema to self-expression. However in a stuffy changing room in August, with lighting that makes you look like the "before" image in an ad for cosmetic surgery, those killer sartorial instincts can be about as sharp as a pom-pom. That grey suede dress is going back.

Susannah Frankel is away.