If you are looking for more power in your swing, then you want to increase the separation between your upper and lower body. Your ability to wind your upper body over the resistance of your lower body helps create a rubber band effect that creates speed on the downswing. This exercise will not only help you create that separation in your upper and lower bodies but will help increase cardiovascular endurance.

Stand with your feet together holding a club above your head.
Step out to a shoulder width stance with your right leg, stabilize your lower body and twist your upper body to the right.
Return to the start position and repeat on the opposite side.
Keep the club above your head the entire time to get your heart rate pumping to build cardiovascular endurance.
Do 8 to 10 repetitions on both sides.