A good suede boot has a feel before it has a fit. Run a hand across the toe and you should feel a proper grain, a nap that changes shade depending on which way you brush it, not a flat sheen that looks painted on. Pick it up and there should be some honest weight to the sole, without it feeling like you're lifting a brick.
If you don't own a pair yet, start with an ankle boot in a mid brown or soft grey rather than black, with a low block heel or flat sole and nothing fiddly going on, no buckles or zips doing a job they don't need to do. A chelsea shape is the easiest to get right first time, because there's nothing on it to go wrong, no hardware to tarnish, no seam sitting in an awkward place. These boots do their best work from October through to about March, over jeans on a cold morning, under a coat when it's too chilly for bare legs but not quite proper winter yet, with a dress on the days you can't be bothered with tights. They're not built for standing in a downpour, suede and standing water have never got on, but for the long stretch of ordinary damp grey weather, a pair like this covers more days than almost anything else you own.
What separates one that lasts from one that looks tired by November usually isn't visible on a screen. Cheap suede is often sprayed to stop it marking, which also stops it breathing, and it goes shiny and a bit plasticky at the toe and heel within a few wears, exactly where you can least afford it. Good suede has a thicker, more even pile, with the colour running through rather than sitting on top. Look at the stitching round the welt, it should be tight and regular, not loose loops waiting to catch. The sole wants to be stitched as well as glued, and any buckle or zip pull should feel like metal, not like it would bend under a firm look. Turn the boot over too. A sole finished properly, with real tread and no rough edges, tells you more about the whole boot than the upper does.
Buy well once and a suede boot will cope with a brush, a wipe and the odd bit of weather. Buy badly and you'll be replacing it before the cold has even properly set in.