What you need: 3 tees, 2 balls, a putter.
Set up: Place one tee into the green then walk 10 feet (three big steps) and place another tee. Walk another 10 feet and place the third tee. The three tees should be in a straight line.
From the first tee, putt one ball past the second tee but shy of the third tee. Then, putt the second ball past the first ball but still shy of the third tee. Grab the first ball and putt it again from the first tee. This time, putt past the second ball but shy of the third tee. Continue this until you leave it short of the previous putt or long of the third tee. See how many times you can "overtake" the previous putt. This dials in your speed control for those 10-20 footers. You can also play this game in reverse (putt shorter each time) for additional practice. See how many "overtakes" you can do!
Inspired by Rob McGarr on Youtube