The moment of truth in the golf swing is when the club impacts the ball and using an impact bag will help you get the correct feeling of impact
Stop thinking about how far back to take the putter or how hard to swing, your mind can do that automatically, and you can prove this by practicing your long putts by just looking at the hole and stroking the putt without looking down at the ball
Maintain a constant posture throughout the entire swing so that your body does not move towards the ball during the swing and cause the heel of the club to make contact with the ball