youcan do all the things these people said but if you are already in pretty good shape, your vertical won't go up alot. Vertical jump is more of a natural attribute then a built up one. It has to do with how fast your muscles can "explode" into movement. The biggest thing that will help you is losing excess weight and toneing up your body, keeping limber, and focusing some on lower legs like calf muscles. Practice your jumps and I also used to do jumping excercises like jogging and jumping on my toes. It strengthens and balances your muscles and connective tissue. Quads do help with vertical jump but like anything, if they are too massive and too tight, then of course its going to hamper your jumping ability.
one person was right though, rebounding has little to do with jumping and more to do with position. Dennis Rodman was not that tall (in relation) and coudn't jump, but he fought like hell for position. Those 2 seconds before you jump for the ball are critical.