Make the second putt!
Seriously, the key to eliminating to 3 putts is to focus on the speed of the putt so you can hit it the right distance. Too many golfers focus on the line of the putt to the hole when one should be focusing on a line that is even with the hole, speed will always dictate how much the putt will break.
So to help judge the distance, make one practice stroke that is way too hard for the distance, then one that is too short and then one that is between them. When you practice, focus on hitting long putts and ones within 4-5 feet of the hole