If you're holding an ankle boot in the changing room and wondering whether it's the sensible one or the interesting one, go sensible first and let the interesting ones be your second or third pair. A boot that sits right at or just above the ankle bone, in a leather or leather look, with a heel you can actually walk a full day in, will get worn in a way that the season's more dramatic shapes often don't. Everything else you buy after that can afford to be a bit more opinionated.
In the shop, sit down and actually bend your foot, because that tells you more than standing still ever will. Check where the top of the boot hits your leg when you walk, not just when you're posing in front of the mirror, since a boot that looks neat standing can suddenly cut across the widest part of your calf the moment you take a step. Look at the zip too, run it up and down a few times, because a stiff or shallow zip is the single most common reason a boot that fit in the shop becomes a boot you fight with at home. Press a thumb into the insole as well. If it feels like cardboard now, it will feel like nothing at all in three months.
The difference between a boot that lasts and one that disappoints usually comes down to what you can't quite see on the shelf. Real leather or a dense, well finished synthetic will keep its shape around the ankle instead of creasing and sagging within a few wears, and a leather sole or a proper rubber one will outlast a thin unit that wears through at the ball of the foot by Christmas. Stitching along the welt, rather than everything held together by glue alone, is what stops the sole parting company with the upper on a wet pavement. Hardware matters more than people admit: a zip pull that feels flimsy in the shop will be the first thing to snap, usually while you're already late. A well made pair also smells faintly of leather rather than solvent, which sounds like nothing until you've owned the other kind.
Once you've got a reliable pair, they'll sit happily under straight jeans, with a midi skirt and thick tights in the colder months, or under a simple dress when you want something less obviously dressy than a heel. They're less convincing with anything very wide legged, since a flare tends to swallow the shape of the boot entirely and you lose the whole point of having bought it.
What they won't do is replace a proper winter boot in genuinely filthy weather, so don't expect them to see you through a flooded car park and still look presentable by lunchtime.