Both weight training exercises and explosive leg exercises such as short sprints and plyometrics can improve explosive power. Remember to work within your own limits. As these are both very demanding, avoid if you have a low fitness level, or any injury. For your sprint work, try and do the sprints on the court you play on, wearing the same training shoes you play in. There are many variations, however keep them short as for your sport.
Shuttle sprints , from baseline to serving box and back, then up to the net and back.
You can repeat this with either no rest or short rest. For best results run against a partner. As above but sprint forward, and run backwards coming back. Try timing yourself. Partner Ball Throw, Stand with your back towards the net or wall, with your eyes shut, have your partner throw a ball in the air behind you somewhere.