A question I answered on Quora: What the fastest way to train vertical jump?

A: Basic answer: Train your legs for explosivejumping. Note that explosive jumping, like what you need for dunking a basketball, is not the same as the jumping you’d do for skipping rope, for example.

When it comes to the actual training, there are myriad programs, systems and recommendations out there, so I’ll make my advice general and simple for you.

Practice jumping explosively. Play b-ball and jump for the rim. Box jumps. Hurdles.
Train your legs for explosion in the weight room, with lifts (squat, deadlift, calf raises, etc) that utilize heavy weight that is heavy enough to challenge you but not so heavy that you can’t move it explosively.
Train your upper body for explosion. Dunking is not just in the legs. You need your arms and core activated as well for it. If you were to jump really high right now without a ball, notice how you use your arms to propel you upward. You can simulate this in training with medicine ball tosses straight up in the air (probably donthis outside, and watch out for he falling ball!).
Train for speed. In b-ball, you’ll often be running before your dunk attempt; the more speed you can build up, the harder and higher you can explode (thibknof an airplane on a runway, for example). Jumping rope helps train for speed and quickness. You can do sprints with a speed parachute strapped to your waist (one of my favorites for speed training). Same for a weighted vest. Sprint up inclines like hills, bridges and treadmills in high inclines and stair master machines.
Make your body aerodynamic. In other words, be in shape. Don’t be on the court with a beer gut, wondering why you can’t jump high. Reduce body fat and build lean muscle. Simplest ways: Eat right (use your best judgement at the dinner table), reduce/eliminate processed food intake (google these if you need help) as much as possible, drink lots of water (not juice and not sports drinks — just water). Make your body look like what you’d call an “explosive athlete”.
Take care of your body otherwise. No alcohol or illicit drugs. Get ample rest (8+ hours sleep daily).

All that should be a good start. For specific programs, see Vertical & Dunking HoopHandbook by Dre Baldwin and The Ultimate Athlete: Off-Court Basketball Athletic Training Program by Dre Baldwin