The one thing I work on most is the drum stroke. I think it takes a lifetime to master. A drummer needs to have a great stroke, with superb dynamic control so he can play everything from the quietest ghost note to the loudest rimshot, and everything in between, at any time, without even thinking about it. For me this is accomplished by exercises such as gripping the drumstick as you normally do, then squeezing the hell out of it, and with zero forearm movement, (matched grip) do single strokes from the wrist while squeezing as hard as you can maintain to both build and stretch your drumstick holding muscles. Aim to make the muscles burn. Of course during actual playing, relax relax relax. Another great tip I learned from a teacher is to imagine a length of string strung between your 2 sticks. Now imagine this imaginary string stapled to the snare drumhead, loose enough so it can slide underneath. So when you raise 1 stick away from the head, it will pull the other stick towards the head. This will give you an incredibly even single stroke roll. For me stick control = hand exercises while doing single strokes at different speeds.