When it comes to hitting a kick serve in tennis, I think the key is to get the ball toss just right, so it's a bit higher and more in front of you than a regular serve. For me, this means tossing the ball about 6-8 feet in the air and slightly to the right of my body, so I can make contact with the racket at the peak of the toss. As for racket pronation, I try to use a lot of wrist action to generate spin, snapping my wrist downwards just before contact to impart a lot of topspin on the ball, which gives it that massive bounce.