It may seem counter intuitive but the more relaxed you are, the better you will swing. Stiffness, especially in the upper back and shoulders, is a pivot killer.
One of the more common things I see in the golf address stance is the stiffness.
If you want clear and convincing proof that the golf swing, any swing in fact, is powered not by the arms but the legs and hips, just watch this javelin training clip.
When I did, I saw something even I’ve never noticed before (not that I sat around watching javelin throwers, I was always on the track when I competed, no field except for high and long jump).