Putter, Practice Hole, 3 Balls, 3 Tees, some sense of distance
Make a lot of puts, build confidence, stop thinking, simulate pressure puts
Set up each tee as a marker at 3, 6, and 9 feet from the hole. Put each ball from the 3 foot tee. If you make all 3, you move to 6 feet and continue. When you make 9 putts in a row you are done. Each time you miss a putt, you have to start over at 3 feet.
This is the best putting drill I have come across. For starters, it really replicates pressure putt situations from real golf. When you are trying to close out this drill, you'll have plenty of adrenaline pumping through your veins. Also, given the nature of the drill, you'll be making a lot more putts than you miss so it really works well for your confidence. Lastly, when you get into the flow, you will stop thinking about your putts. You will be dialed in and just have a fluid putting motion. I think that not thinking is the key to putting well and this really helps to accomplish that.