This is a variation on the putting gate drill; I have found that this irritating drill produces better results, faster. The drill itself is very simple, setup three golf balls so that the two outside balls are just larger then the length of your putter heel to toe. Now putt hitting the middle ball only.
Replacing the two outside balls begins to get irritating very fast and you learn quickly how to groove your stroke. I’ll tell you a secret with this drill: If you keep your eyes focused off the golf balls entirely, you will achieve success more often. It’s interesting, but by focusing on the grass between your putter and the center ball your results will improve. This will anchor your eyes and your head, reducing their movement throughout the stroke.
This is a great drill to practice and improve your short putts and ingrain a repeatable, dependable putting stroke.