In this video you will not only find interesting exercises but also the right kind of tips to choose an exercise ball. While buying one you have to be sure that the size it right and this can be done by ensuring that your thighs are parallel to the floor when you sit on the ball.
One exercise to start with is a simple one where in you have the fitness ball between your back and a wall or any other support, then you simply need to go up and down bending your knees. The routine is good for your quadriceps, hamstring as well as calves. You can perform nearly 15-20 reps for this one.