When my putting goes AWOL i spend an hour on the putting green doing Butch Harmons "kicking a field goal drill". If you dont know what it is, find a flat part of the green and place a marker 1 to 2 metres from the hole. Approximately at the half way distance between the marker and the hole place two tees allowing the enough room for the ball plus a bit so that the ball can run between the two tees. as you get better at it you can reduce the space between the two tees. This drill gives you excellent feedback on whether your putter head is closed (the ball will hit the tee on the left if you are right handed) at impact or open (the ball will hit the tee on the right). This drill also teaches you to pick a spot on the green between you and the hole and bulids your confidence when putting. Ther is no need to think about the hole because as long as you kick the field goal the putt will drop. I showed this drill to a friend who has averaged 33+ putts per round with instant success.