Jump serving is an advanced volleyball skill, which is why I would only recommend this instructables for advanced volleyball players. A serve starts every play in volleyball, which is why it is important to know how to do it if you want to play volleyball.
Step 1: Toss
The first step for jump serving is tossing. Make sure to toss the ball high enough in front of your right shoulder (or left if you are a leftie).
Tips: Try out different types of tosses. Try tossing with your right hand, with both hands and with your left hand and then decide what feels best and is easiest for you. Toss the ball high enough in the air so that you can make contact with it at the highest possible point.
Step 2: Approach
After you have tossed the ball in the air, approach. Use the approach that you use for hitting, so take three steps: left-right-left. Make sure to have a fast and dynamic approach to be in a better position in the air for hitting the ball. (If you are a leftie, your approach would be right-left-right.)
Tips: Make sure to use your arms to have more momentum in order to jump higher. Using your arms will also help because you will automatically have your arms up, ready to hit the ball.
Step 3: Hit
Once you have tossed the ball, approached and jumped, you will have to hit the ball. You will probably not be able to hit the ball properly the first time you attempt to do a jump serve, but that is ok. Make sure to work on your timing and try out different heights to toss the ball. (Just try to find what is best for you - the timing part of jump serving involves a lot of practice).
There are different types of serves. The most popular ones are float serve and topspin serve. For a float serve, make sure to hit the ball at the back. For a topspin serve, make sure to hit it a bit higher so that it will go down. (If you imagine an equator on the ball like on the earth, for a float serve hit it in the middle of the equator and for a topspin serve hit it north of the equator - just make sure to not hit the ball at the right angle so that it will still go over the net). This may also require a bit of practice, so don’t worry if you can’t do it on your first try. Tips: Try to make contact with the ball at the highest possible point. This point will depend on how high you toss the ball and how high you jump. Hit the ball with your flat, opened hand (make sure your fingers are apart). When you make contact with the ball, make sure that your arm is straight. Make sure to maintain your body tension in air so that you will have enough strength to hit the ball. Make sure to swing your arm through entirely, don’t stop the motion after you have contacted the ball.
Step 4: Landing
After you have hit the ball in the air, land on your feet. After you have landed, make sure to assume your position in the back-row defense. Depending on what system your team plays with, this position can be anywhere in the back row.
Step 5: Additional Tips
1. Try to create a ritual before tossing the ball. A ritual can help you increase your focus and help you to be confident. Coaches will sometimes try to disrupt a server’s confidence and focus by taking a taking a time-out, making a substitution or disagreeing with the referee's latest call. If you have a ritual you do every time before serving the ball, it will help you to focus and keep your confidence level up. A ritual could be very short and simple or a bit longer. Some people choose to bounce the ball a certain number of times (like I do in the picture), whereas some choose to talk to themselves and say a specific phrase to keep them focussed.
2. Take a few tries to find out what is best for you. If you feel more comfortable doing a float serve, continue working on your float serve. If you feel more comfortable doing a topspin serve, do a topspin serve. If you prefer to approach the backline at an angle instead of in a straight line, then feel free to do that (although you will have to make sure that you have enough space behind the court to do your approach so that you will not touch the line before jumping). As I already mentioned above, make sure to try out different ways of tossing the ball (using one or both hands). Another thing you can try out is starting from different distances from the backline. Maybe you will start very close to the backline because you have a very short approach, but maybe you will start further away from the backline because you have a longer approach.