Good... nice swing, toss, prep, and trophy.
Bad... rocking onto your heels can cause you to footfault when going for wide slice serves on important points. Try not to.
Bad... poor forward movement towards the opponent. You end up basically ON the baseline ready to play a defensive shot....but you are serving!
Bad... tendency to serve as if you're just going thru the motion, rather than to concentrate on the motion FIRST, then go into your motion. Take some time between serves! Notice the top players, for important points, tend to stand really STILL, bounce the ball lotsa times, THEN go into their motions. Every serve should be considered in "important" point since you can win with it, cause errors on the return, or cause the opponent to set you up with a weak return. Take your time!