This story is for you if...
1. You always read your putts from behind the ball...
2. ...even on severely sloping greens
You're missing badly on breaking putts, which leads to fewer birdies and pars and more bogeys. The simple reason for your struggle is poor green-reading technique and alignment.
If you want to get a proper read, you need to look at the putt from behind the line you plan to start the ball on, rather than the one that runs directly from the ball to the hole. To do so, pick a spot where you think the apex of the putt (maximum break) will be and examine the putt by looking from behind your ball to that spot. Set the putterhead square to the chosen target line and then walk into your setup, always keeping in mind that your actual target is the apex of the break, not the hole. Stroke the putt to this spot without being distracted by the actual hole. Use this technique consistently, and your green-reading as well as your results on breaking putts will improve dramatically.
Finding your ball-to-apex line is only half the battle you must also be able to align your putterface square to it. Any good putter will feature effective aiming lines. If yours doesn't, consider purchasing a new model. I designed a line of Coutour putters with a large arrow on the back end to help you point your putter easily and consistently. For more info, visit coutourgolf.com.