The Jump Serve
The Jump Serve is one of the most overly glorified skills a player can learn. Used effectively, it can throw the receiving team off balance and cause them to run their first offensive posession out of system. This gives the serving team an obvious advantage in the rally, as a team out of system has less options offensively and thus is easier to defend.
I am approached by high school level players quite often, asking for advice on how to improve their jump serves, or to teach them from scratch. My response to this question is always, "Learn to float effectively and accurately to spots on the court first." However, once this skill is learned, the next question is whether or not the player uses proper attack footwork. This is essential to a consistent and effective Jump Serve.
For the purposes of this post, I am going to assume you already know the proper four-step attack approach (with regards to a right-handed player.)
Jump Serve Technique:
With adequate room for your full attack approach between yourself and the baseline, hold the ball with your serving hand in front of you with your palm facing up. Toss the ball up and in front of your body with your first step (right foot if righty, left foot if lefty). You can try putting a little topspin on the ball with your toss if you like, most players do.
The goal of the toss is to give yourself enough time to take a full attack approach towards the ball in order to attack the ball at the peak of your jump. This is probably the most difficult part to learn, as it takes a decent amount of experimentation for new players to know how high and how far in front of themselves they need the ball to be tossed. The consistency of your toss will dictate the consistency of your serve (assuming you are consistent with your attack form, of course.)
Once you have tossed the ball in the air, take your full attack approach remembering to put a lot of effort into your jump and attack the ball. Unlike when you are attacking at the net (or from the 10 foot line/attack line for more advanced players), you are not aiming to get on top of the ball. For lower level players and those who are not as powerful, your goal is to contact the bottom of the ball and aim your swing upwards towards the ceiling. Taking a full swing, remember to have a quick wrist snap in order to generate the necessary topspin to keep the ball dropping quickly to the court and in-bounds.
For those players who can generate more power on their swing, you can try more and more to get behind the ball and really drive the ball hard. But the key is to always snap the wrist hard, as the topspin will keep your serve in the court.
Pros and Cons:
The jump serve, while intimidating to players who don't see it often, is actually a very easy serve to pass. It generally moves in a straight line and has enough velocity that the receiver need only get behind the ball and make sure they make a clean contact. No additional movement is necessary. It is also a much more difficult serve to master, and to execute consistently, due to all the additional moving parts to the technique. This is why I generally will stress the importance of learning an effective and consistent float serve at lower levels of play. It is generally more effective at the high-school level to serve to specific targets on the court (picking on weak passers or keeping the ball away from the stronger hitters) than to just serve the ball hard.
However, at higher levels of play the jump serve can be a true weapon. With enough power behind it, even the best passer will have difficulty getting their body behind the ball to make perfect contact. Driving a team out of system is the key to winning points on your serve. Winning points on your serve is the key to winning at volleyball.