If you are trying to improve your vertical leap then there are a number of techniques you can use to have the most impact. If you play sports such as basketball and volleyball then a good vertical is essential so following a system for strengthening your jump will vastly improve your game.
To start, it is important to mention that you should not overwork your leg muscles. You do not want to cause any long term damage or halt your training for any period of time. So make sure you are not training excessively.
One great exercise to use is the lunge. But in order to have the maximum impact to improve your vertical you should leap up in between each lunge in an explosive movement. This fast movement is what strengthens your leg muscles and improves your leap.
Calf raises are also great exercises and you can perform these on a staircase. The staircase can also be used for running up which is great exercise but particularly good for working your leg muscles in a way that will benefit you for your sport.
Squats are also great when you add in the element of explosive movement. Go down slowly and then push up in a fast and dynamic movement. This will again equip you well for leaping for a dunk or spike.
If you work on these exercises you should see improvements when you move onto the court or sports field. Make sure to monitor progress so you know exactly where you are and how much you have moved along. This should help to motivate and encourage you when you can see the improvement.
If you want to check out a complete system which goes into a lot more detail then take a look at the site below and check out the video.