Posture
Purpose:
From a safety standpoint, the straighter the back the healthier it is for longevity and enjoyment of the game. Also, the club is less likely to be manipulated off-line by the arms and hands if the back remains straighter at address. Allow yourself to turn (rotate) around the spine for your takeaway.

Drill:
Use Club To Aid Posture

Instruction:
Stand straight up with feet hip width apart, knees slightly bent and the club placed vertically along your spine. Try to get the spine as flat as possible to the shaft.
 
Hinge at your hips, bowing forward to see the ball while maintaining your straight spine against the club.
 
Bring your club down to address the ball. You may even try to hit balls using this drill.