Before any training, always stretch and warm up the whole body to avoid injuries!!
The first training should be to get comfortable sitting on the ball. Slowly try taking out both legs off the ground and letting the pressure of your weight down around the coccyx and two hip bones of the butt. Do not bend the lower back too much (although it may seem easier, it surely will give you back pain later). Done that, fell free to experiment moving a little bit and as long as you can maintain this position easily, you may move forward to the next step.
Now that you feel more confident with the ball you may stand on your knees on it. It's not a big deal and most of the time are just afraid we will fall and hit our head somewhere, but the truth is that when we let go of the fear, the movement is quite easy and it's just one more step to the standing position we aim. First place one knee on the ball and, helping with your hand, place the other one as well. Don't place them too close to each other, not to far apart (but the closer, the harder). A nice tip, that will be helpful to the standing position as well is not to contract the body too much. Be relaxed and try acting as if you were on the ground. You may start holding to a wall or bar, but I wouldn't do it because we tend to get use to help like this. Try moving up and down from the kneeling position to a traditional 'seiza' japanese sitting position, that will help getting the body use to changes. Once kneeling is not a difficult thing anymore, move to the last step.
If you got here, you might already have a great balance, but the last step is also the most challenging one. I recognize three best ways to step up on the pilates ball and they will be presented considering their difficulty. First, holding to a parallel bar where the grip gives you stability, pull you body up sustaining your weight totally on the arms (like a regular pull up) and slowly move your body down on the ball with both feet spread more or less following your shoulders distance apart. The second way is a little harder, but as long as you know your way along the kneeling position, you should not have major problems. From the kneeling position, bend to one side a little, counter pressing the ball with your hands, and take one leg out. Place the leg, now with your foot on the ball, slowly and try maintaining this position half kneeling, half standing. Do the same thing with the other leg and slowly stand up.
The last, and most fun, way to stand on the ball is just to jump on it. The jump must be precise and remember not to bend much the knees when jumping, otherwise it you be much harder to land properly on the ball. For now I only recorded this last jumping move on camera, but maybe I'll record the other steps.
This training helped me a lot and I feel much more grounded and safe performing any kicking and more advanced martial arts techniques. I've also applied this training to my students and awesome results followed. I hope you liked this tutorial and more will come soon!