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
The width of your legs in your set up is important because it allows for the legs to function properly so that your right thigh can catch up to your left thigh creating the correct downswing and allowing for increased power
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