Even great players have a common posture-related putting flaw: chasing the ball down the target line by moving the rear shoulder forward during the stroke. This will make you pull a lot of putts or hold the face open through impact to compensate -- another recipe for inconsistency.
Practice hitting putts with just your rear hand, holding your front hand gently on your rear shoulder. It's OK for your shoulders to rock up and down as part of the motion, but make sure you aren't feeling that rear shoulder move forward, toward the ball, during your stroke.
