Very first thing is to pay attention to the toss. The toss of the ball is completely different from hitting slice serve or flat serve. The Ball toss has to be behind you which is around 10-11 o'clock direction above you head. http://www.youtube.com/watch?v=TkAj6MmwxHw
you got to have the right lean and a decent wrist action upwards to create enough top spin. if u lean into it and brush it will go pretty fast and jump, but first get the toss right. the wrist action determines how much kick u got on the ball.