If you can't turn your lower body independently of your upper body (the pelvic-rotation test), then you'll likely swing "over the top" of the target line from outside to inside on a steep angle. This causes sliced or pulled shots. You want to swing down from inside the target line.
1. The Problem: Over the Top
Do two sets of each exercise (eight reps); repeat in the opposite direction if movement is to one side.
Keeping the upper body facing forward, hold a medicine ball and step up, rotating your hips to the side.
Supported Stork Turns
Hold onto a club and stand on one leg. Keep your shoulders square and rotate your pelvis back and forth.
Reverse Clam Shell
Lie on your side, legs together. First separate your legs at the knees. After a set, separate your legs at the hips and repeat.