Weekend golfers frequently fight a slice because their right shoulder moves out over the ball on their downswing. If you struggle to keep your right shoulder from moving out over the ball -- a common error for players who swing "over the top" -- a few simple steps can help you alleviate the problem.
Correct your thinking. Most golfers think about swinging up on their backswing when they should think about swinging around their spine. Consider this: If you stand erect and swing around your spine, you swing parallel to the ground. If you tilt your spine forward and make the same swing, your swing moves up during your backswing and down during your forward swing. The tilt of your spine when you address your golf ball automatically creates the up and down motion you want. It should improve your balance as well.
Start your backswing by turning your shoulders. Again, think "around" rather than "up and down." Your spine tilt will take care of the upward motion, and your shoulder turn will keep you from lifting your shoulder during your backswing.
Keep your knees -- especially your right knee -- flexed. When players come over the top, they usually straighten their right knee. That pushes their right hip upward, which also pushes their right shoulder upward. Keeping that right knee flexed will help keep your right shoulder on the correct plane. It will also help you develop a stronger coil behind the ball. You can practice this movement without a club simply by taking your address position and crossing your arms across your chest, with your right hand touching your left shoulder and vice versa. Practice full shoulder turns back and through while keeping your knees flexed. PGA pro Frank O'Connell recommends this drill to teach proper body movement and balance while developing power.
Start your hip turn (and therefore your downswing) by driving your right knee toward the ball. Tom Watson says the average player hangs back on his right foot too long, and that this causes him to throw his right shoulder toward the ball. He says pointing your right knee at the ball during your downswing creates a better weight shift and prevents throwing your right shoulder.
Drop your right elbow down near your right side during your downswing. If you point your right knee as Watson suggests, this is a natural result. In his book "Five Lessons," Ben Hogan illustrated this effect as happening almost simultaneously.
Hit the ball. From this position you can swing without worrying that your shoulder will move out over the ball.