The key to hitting a golf ball a long way is minimizing your hip turn and maximizing your shoulder turn. The easiest way to accomplish this is to make sure that your left knee doesn't slide to the right on the backswing and that the right knee stays firm and flexed throughout. (Opposite knee for left-handed players.) Also, get your shoulder behind the ball at the top of the backswing. This ensures good weight shift and allows for a longer swing.