In golf, like other sports, it is critical to be relaxed to perform at your very best. A sure sign of tension in your golf swing is a sudden, jerky downswing with no rhythm or flow.
A great way to acquire a graceful, powerful downswing is to improve the quality of your follow-through. When you practice, concentrate on achieving such a full, free finish that you actually whack yourself on the back with the club shaft at the completion of your swing.
For whatever reason, the freedom needed to do that transfers wonderfully into the downswing