On a straight putt, put markers down at 3, 4, 5 feet. Starting at the 3 foot mark, drain 3 putts in a row, move to the 4 foot mark and drain 3, move to the 5 foot mark and drain the final 3. Goal is to drain 9 putts in a row and if at any time you miss, start all over at the 3 foot mark. That last 5 footer does a great job of simulating pressure.
You can add variations to this to make it harder: first putt has to hit the back of the cup, second putt has to be perfect speed, third putt has to barely go over. Another is to do this on breaking putts. You can also go a step further by adding the varying speed to breaking putts <- very difficult.
Once I'm able to complete the 9 in a row, I stop. Even if it's my first attempt. Keeps the confidence up, and your last memory coming off the practice session is a positive one. Also I think it's important to go through the entire putting routine to help make the session feel more like what you'll experience in an actual round.
