First practice a soft landing or you can get yourself in deep trouble because no matter how long you jump, the gravity pulls you back on earth. So, an awkward landing may keep you out from the sport for long. Before jumping twist your ankle clockwise and anti clockwise.
After warming up, you are ready to start the intense part of the training. So, start by jumping from a height. Let this be a low chair or stool. First, you can jump (or rather, jump) on two legs, but generally you need to learn to do it on one leg. With this exercise, you develop ankle, knees and shins muscle. Twenty of these jumps a day would be sufficient. Of course, you need to soften the maximum load on the leg on landing.
The third and last phase of your workout is to try and touch the ring. Find a suitable place to practice this or you can take classes. This can be done not only in a gym but a normal park with tall trees. In the first case you need to work off a jump to the ring with a shaking leg, scattering and jumping. While in the park, look for a more or less thick branch on the height of the ring and try to jump up to get it.