The point here is to sit on something unsteady. By doing so, you engage your stability muscles which help you keep your balance. These muscles are the ones we want to get stronger.

1. In the beginning, I would suggest sitting on a soft mattress with your feet touching the ground. Then, while making slight movements to get your body off-balance, your muscles will work harder to keep you from falling.
2. Once the mattress becomes easy, move to something more difficult—like an air mattress slightly depleted of air—to make it more unsteady.
3. If once again this becomes easy, sit on a balance disk, and create movement. You can kick a rolling ball or just lift one leg up while keeping balanced. You may turn side to-side or clap your hands or you can pick something up from the ground to make it more challenging.