When you rotate your arms to do the backswing, let your shoulder follow naturally. Then let the rotation continue naturally to your hips, then to your legs, and feet. This rotation and coiling of the body should be a smooth continuous body movement.
When you have done a full backswing, start to unwind or uncoil your body naturally in one fluid motion, but this time start from the bottom. Uncoil your feet and legs first, then your hips, and finally your shoulders and arms. Make sure that the work is being done by your hip muscles and not your back muscles.