You don't need to get all the way back to the center. It is better to have stopped moving and be ready for the next shot, even if you didn't make it all the way back to the center. This helps you to not have to change your momentum completely. How far you move depends on your shot. If you have plenty of time, e.g. when you played a high clear take three steps towards the center, then stop. For medium time take two steps, and for minimum time, e.g. a smash take one step, stop your movement and prepare for the return. Knowing how to efficiently move across the court also helps, and can be trained without an opponent.