At first, you can place your calves in front of you so that they are touching the ball. This will give you added stability while learning to use the ball. Later, you will want to move your calves so they are not touching, which will provide more benefits for your core.
If you are using a computer, make sure it is at a 90 degree angle. If it is not, your neck will be out of alignment with the rest of your spine, and the ball will be less useful in helping your posture.
Work up to 30 minute intervals as you get used to the chair. Doctors do not recommend that you sit for longer than 30 minutes at a time. If you need to get up to change chairs frequently, this will also benefit your spine.
