Stand two women in blazers across a room and you will spot the difference before either of them says a word. One jacket sits flat across the back and skims the hip, the other pulls across the chest with a button straining for its life and a collar that gapes at the neck. Fit does more for a blazer than almost anything else you put on, and it costs nothing extra to find the one that actually sits right.
For colour, you are usually better off starting with the ones that behave rather than the ones that shout. Navy, black, a soft grey or a camel will go with nearly everything you already own, and a check in a muted tone gives you a bit of interest without fighting the rest of the outfit. Bright colour and bold print are lovely, but they ask more of you, because they want to be the main event and everything else has to step back and let them.
How it ages depends mostly on what it is made of and how you treat it in those first few wears. Wool and wool blends hold their shape for years if you hang them properly and let them rest a day between wears rather than piling straight into a bag. Cheaper polyester blends tend to go shiny at the elbows and lose their collar roll within a season, so in the shop, scrunch the fabric in your hand and see if it springs back or sits there creased. Press seams with a cool iron and a cloth rather than direct heat, and get the sleeves taken up if they are long, because a blazer with sleeves past the wrist bone reads as borrowed, not chosen.
Honest limits first. A structured blazer is not kind to very hot weather or to anything that needs to move freely, a long walk, a dance floor, a day chasing small children, and it rarely works layered over anything already bulky, since two structured shapes fighting for the same space makes you look bigger rather than sharper. If you want softness and ease, an unstructured jersey blazer or a cardigan will serve you better than forcing a stiff one to do a relaxed job.
It also clashes with itself more than with other pieces. Big shoulder pads under a big collar, a bold check jacket over a busy printed top, heavy jewellery piled on top of strong lapels, all of that competes rather than complements. Keep what is underneath simple and let the jacket carry the look.
Thrown over a plain t-shirt and jeans you already own, a good blazer makes the whole outfit look like you planned it, even on the days you really didn't.
