How to feel a good shoulder turn
The modern swing is simple. It's basically just turning back and turning through, with less tilting and lateral movement. But I see too many golfers who don't understand how their shoulders should turn with their bodies. Try this exercise to feel the proper move. It generates more power and consistency—and is easier on your back.
Stand up straight and put a club over your shoulders, across the back of your neck (second photo). Then rotate your shoulders so the club stays horizontal on your backswing twist and your follow-through twist. Your shoulder line is perpendicular to your spine angle throughout. Now transfer that thought and sensation to your address posture (larger photo). Turn your shoulders back and through on a level line, the way you did standing tall.
Again, your shoulder line should remain perpendicular to your spine angle. That's crucial. Your club will swing pretty much on the same path.