While most teaching pros advocate maintaining your spine angle during the swing, others prefer to phrase this as keeping your forward bend at the hips. The difference may seem like mere semantics, but it could help you achieve this critical fundamental.
First, note that you should bend at the hips, not the waist. Bending from the hips promotes a straight spine and easy rotation of the hips and shoulders, while bending from the waist causes the back to arch. This makes it difficult to turn properly and can lead to injuries.
Another note: Tests show that the average tour pro sets up with a bend of 36° forward from the hips. The typical amateur bends either too far, then lifts up during the swing, or not enough, forcing him to crouch or lean forward to hit the ball. Both actions produce ugly results.
To check your hip bend and posture, stand with a full-length mirror to your right (for a right-hander) and set up to a ball. Ideally, the shaft will intersect your body at a 90° angle. Teachers also recommend tilting the spine slightly to your right at address, about 5°.
This allows you to transfer weight to your right side on the backswing. A good way to maintain your hip bend is to visualize your head propped against a wall at address, then keep it touching the wall from takeaway to finish.