There are certainly a great many factors that come into play when working on your vertical leap. At this point, though, it sounds like the first thing you need to do is to strengthen your shin muscles. Do toe raises—first, withjust the weight of your body, then with additional weights (dumbbells in your hands, weight belt,
standing calf raise equipment, etc).
The next stage is to leap and land on the balls of your feet. Focuse on minimal heights to begin with (like Ralex recommended, just jump over a broomstick)—up, down ... side to side ... front to back. Don't do too much too soon.
When you get to the point that you no longer get
shin splints while hopping around like a rabbit for 10 minutes, let me know (then we'll talk about hip flexors, lower back, etc).