While my wrists are fine in general, some of the more strenuous exercises I (try to) do are painful sometimes; for example, one-armed pushups. I used to have more problems, even when doing pull ups (at the bottom of the movement) and for all kinds of pushups.
To avoid this I started doing pushups on my knuckles and also did some simple wrist exercises (basically, holding my fist tight and moving the wrist around in various ways). In general, this helped, but I've obviously still got problems and I'd like to "fix" this permanently. I understand that wrists are mostly tendons and not muscle and I'll time to improve, which is why I want to start early.