It has been a week of threes, so here’s another.

The first three was a way to compare high-street and designer purchases: analyse your feelings and rank the item for design, quality and branding. The order should help you make your decision. The last should probably be closely followed by one of the others to make it worth it, unless you feel like a guilty brand buy-in.

The second three was the aesthetic that unites casual and formalwear: the harmony of cut, colour and pattern is the same whatever an outfit’s intention. Both modern and traditional outfits have stand-out (“pop”) pieces, an intrinsic balance, and cuts that express personality.

The next tripartite analysis combines parts of both predecessors. It concerns shopping decisions, and ranks fit, colour and style.

It’s an old saying someone passed on to me years ago – when you’re buying a piece of clothing only buy it if it fits well. Then consider whether the colour suits you. And only then consider whether it is fashionable/stylish/inspiring.

This is a piece of advice that is hard to disagree with, but also hard to stick to.

A piece of clothing flatters you most when it fits you well. The classic silhouette of a suit is classic because it flatters a man more than almost anything else. Even women that eschew formal wear – and therefore suits – for their men, find they prefer t-shirts, jeans, sweaters that fit well. If a t-shirt is skin-tight, has no waist or has a collar that covers your Adam’s apple, it will look unattractive.

Conversely, if something fits you badly it is always the first thing anyone notices. Colour and style will be ignored, will be blinded if your suit jacket strains against your mid-riff, tell-tale lines radiating from the waist button.

Colour, next, can smother style. (It’s a little like paper-rock-scissors this, except that style doesn’t trump fit – you’d be an idiot to pick style.) No matter how stylish that orange shirt, anyone’s first reaction will be revulsion. Conversely, there’s a good chance they will notice if it fits you perfectly.

There are as many points of advice on colour as there are on fit – bright colours with black look cheap; brown rather than black with blue; reds and greens for those with ruddy complexions; stronger colours for those with darker skin; white makes you look tanned unless you are already too white. These are fairly instinctive but take some deliberate thought, after analysing the fit that is.

A good maxim, but as one hard to stick by. I can’t count the clothes I have that were not bought with fit in mind. Or with fit ignored.

Colour is subtler but gnaws at you. Unsuitable shades create vague irritation rather than specific frustration.

So this triplet is certainly worth bearing in mind. And once you’ve decided it suits you, you can turn to design/quality/branding to decide whether it’s worth the money.