The one thing worth knowing before you buy a denim top is that it's a jacket in spirit even when it's cut like a shirt, so try it on over something rather than alone, because the fabric has a mind of its own and needs room to do its thing.
If you own none, start with a classic shirt style in a mid wash, something with a bit of give in it rather than the rigid, cardboard stuff that makes your elbows feel like they're under house arrest. I made the mistake years ago of buying the stiffest one on the rail because it looked the most "proper", and it crackled when I sat down and left a crease pattern on my arms that lasted an afternoon. What you want is denim that's had the stiffness washed out a touch, the kind that softens where you bend it rather than fighting you. Hold it up and give the hem a little tug, if it springs back hard and flat, it hasn't been broken in at the mill and it won't break in much on you either, not without a fight.
A denim top like this does an odd, useful job in an ordinary wardrobe because it reads as both a top and an outer layer, so it sits easily over a plain T-shirt or a vest with the sleeves pushed up, and just as easily under a coat with nothing showing but the collar. I wear mine open over dresses more than I wear it buttoned up as a top in its own right, which took me a while to admit because I bought it specifically to wear done up. It pairs well with almost anything that isn't also denim, obviously, unless you're going for the matching look on purpose, which has its moments but is not a daily uniform. Soft jersey underneath works best, the kind of fabric that drapes against the stiffer cotton of the denim and stops the whole outfit looking like armour.
On colour, a mid blue wash is the easiest thing to live with by a distance, it goes with more than black does and shows less wear than a pale wash, which bruises at the cuffs faster than you'd expect. Black denim looks sharp for about three wears before it fades unevenly round the seams, so go in knowing that. A soft, slightly worn mid blue just keeps going.
This suits anyone who wants one piece that can look deliberate over a plain outfit without any real effort going into the rest of it.