The Jump Serve can be an effective and devastating serving weapon.  Jump serving is all about doing what is comfortable for you and keeps you consistent.  Take the toss, some people toss with one hand, some with two, some with their hitting hand, some with their off hand, whatever is comfortable, and effective for you is what is best.
   The most important aspect of the jump serve is the toss.  In order to be an effective jump serve you must have a consistent toss.  The toss should be a combination of high enough to give you enough time to get a three step approach in and low enough to force you to be quick and explosive.  The toss should be out in front of you far enough that if you did not approach and hit the ball would land inside the end line.
   The point of a jump serve is to hit a serve hard with a great deal of spin that is difficult to pass.  You have to swing as hard as you can in order to make yourself a good jump server.  Only after you have confidence enough in your toss and approach should you work on changing speeds. 
   A good jump serve is deep along the opponents end line.  The ball should go by the passer about shoulder height and drop in behind the passer.  A jump serve right in front of the passer is actually one of the easiest serves to pass.  But, as you get the ball higher up on the passer it becomes much more difficult to pass.  A jump serve right at the passer's head is very difficult to pass.  The passer must move their feet in order to

pass the ball with their platform to pass this ball.  Attempting to overhand pass a good jump serve is difficult, because of the force and topspin.  You have to be extremely strong to be able to overhead pass a jump serve, and not be called for a lift.  A ball served with good velocity shoulder height on the passer is generally out, but the top spin a jump serve has can keep the ball in. 
  In summary the keys to remember when working on your jump serve are:  a good consistent toss, swing as hard as you can, and hit the ball deep. 

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