Create two lines of pegs aimed straight at the hole from about six feet. Putt through the middle of them, trying to avoid hitting them on the way through. Once you are competent, make it interesting by setting targets. Start off trying to make 25 in a row, then work your way up to 50, 75 and then 100. If you miss, start again. By the time you get into the 90s you will really feel the pressure so the benefits are two-fold.