Hitting the ball with the sweet spot of the putter allows the putter face to stay square and not twist
The arms work very differently in the swing, with the left arm staying straight up to the release and the right arm bending early, use this two club drill to get the feel of the proper motion of the arms working together
With a traffic cone behind you practice your downswing trying to keep the club inside the cone to simulate the correct approach at impact, this will help eliminate casting, over the top and other downswing faults that create curved shots and an improper impact position