Learn an exercise to allow the putter to travel straight back and through on a plane
Read greens by selecting the high point of the putt between the spot and the hole, and let the contour of the green bring the ball into the hole
One of the most common faults in the swing is taking the club back outside, to fix this many players try to control the clubhead but in the swing it is actually the club handle that controls the clubhead so put a tee in your grip and measure your handle distance from your body through the swing