Using Plyometric Boxes will dramatically improve your speed, explosiveness and jumping ability.
Plyometric exercises train your muscles and nervous system to reduce the length of time of the amortization phase. Shortening the amortization phase actually increases the amount of energy you can carry from your approach into the jump, which can have a dramatic effect on your vertical.
From a comfortable distance away from a small plyo box, stand with your feet shoulder width apart. In one motion, jump up to land on top of the box. Step down and repeat. You want to work on making sure that your landing is soft and stable. If you are landing loud or out of control, you are performing the drill incorrectly and should not move to a higher box until you have mastered your landing.
There are different sizes of plyo boxes and you should start with a low height and gradually increase the height as you want to increase the difficulty of the exercise.
One Leg Jump
After you have perfected the regular landing of the box jump, you can move on to the one leg plyo box jump. Start the same way as above, but now when landing you are landing on one leg then step off with the opposite. Get the same amount of repetitions on each leg. Remember that stabilization and a soft landing is important.
The higher the box the more difficult. Start on top of the plyo box and step off. During the landing you are going to land on both feet at the same time in a semi-squat position, trying to absorb the landing force. Once this is mastered you can take a slight jump off of the box and again, stick the landing.