3 Musts:
1 Grip Points to Belt Buckle
Since the takeaway follows from the set-up, a proper address can correct errors before they happen. The height of the hands is critical: If they are too low, the wrists will cock the club up too steeply; too high, and the forearms will rotate the club too far inside. To ensure correct hand height, the butt of the club should point at your belt buckle at address.
2 Clubface Points at Ball
During the takeaway, the hands and arms swing the clubhead up on the same plane that the shaft forms at address. One useful checkpoint is to see that your clubface is pointing at the ball as you swing the club back (right). This will head off two common errors: fanning the clubface open so it points at the sky, or holding it closed so it points down at the ground. Either mistake forces you to become handsy if you hope to return the club back to square at impact.

3 Wrist Cock Blends with Turn
When your wrists begin cocking up, they should blend with your turn to keep the club on plane. You can check this by stopping your backswing when the shaft is parallel to the ground. If it is also parallel to the target line (right), your plane is correct. If the clubhead is either inside of the hands (too flat) or outside of the hands (too steep), your wrists have cocked to the side and altered the plane.