I put off hanging a real mirror for years because every apartment I rented had those builder grade medicine cabinet mirrors that told you nothing useful, and I figured any mirror was basically the same once it was on the wall. What changed was standing in a friend's hallway, catching a full length reflection in actual daylight, and realizing I had been getting dressed by vibes alone for the better part of a decade.
The day it arrives, check the back before anything else, because that's where the whole thing either holds up or falls apart in year two. You want a proper hanging system, a cleat or a wire rated for the actual weight, not two flimsy loops that look like they were added as an afterthought. Run a hand around the frame edge too, since mirrors get knocked in shipping more than people expect, and a chipped corner on day one only gets more annoying with time. Glass thickness matters more than it seems like it should. Thin glass gives you a slightly warped, carnival mirror effect if you look closely, especially at the edges, and you will notice it every single day once you've seen it once. Once it's up, the mirror itself barely changes, glass doesn't age the way wood or fabric does, but the frame is where all the living happens. Wood frames pick up a nice patina if they're a solid species, though cheap veneer ones start peeling at the corners within a year or two, usually right where hands touch it to adjust the angle. Metal frames, especially anything brushed rather than polished, wear well and just need a wipe down, while polished brass will develop spots unless you commit to actual metal polish now and then, which I never do, so mine looks a little moodier than it did on day one. For cleaning, skip the ammonia glass cleaner near a wood or metal frame and just use a damp microfiber cloth, it keeps the finish from clouding over time.
On finish, I'd steer toward warm woods, aged brass, or a plain black frame over anything high shine and silver toned, because polished chrome shows every fingerprint and water spot within a week, and I learned that one the hard way on a bathroom mirror that looked like a crime scene by the second month. A worn brass or a matte black frame hides dust and small scratches instead of announcing them.
Years in, the glass still does its one job perfectly, but the frame softens, the brass dulls into something warmer, the wood darkens slightly, and the whole thing stops looking like it was just unwrapped and starts looking like it's actually lived in your hallway the whole time.