Get a piece of string about 10 feet long and two strong but thin steel pins. Attached the string to both pins. On a putting green find a straight uphill putt. Put one pin in the ground behind the center of the hole and one pin in the ground on the straight line back from the hole. Position a golf ball directly under the string. When you address the ball to putt, you should see the string directly in the center of the ball. If the string is not in the center, then you are standing either too close or most likely too far from the ball. Adjust your stance until the string is in the center of the ball. This also helps give you a clear view of the line you want to put on. Line your putter up directly behind the ball with the string in the center of the putter. Make your putting stroke keeping the putter head moving up and down the line. Practice this drill for 15 to 20 minutes before you play to ensure proper setup before each putt and the proper travel path of the putter head. If you practice this, you will make more putts!!
He gave me this lesson and it has really helped. I have given it to several other people, including Seamus, and all have benefited from it!!!