Several previous threads have addressed this issue. The best advise I have taken away from them, besides the obvious practice is as follows for Tournament greens:
For uphill putts take total distance and subtract 25%. i.e 14' putt + 4" up= 18'. 25% of 18=4.5', so 18-4.5=13.5' should be used to get the ball close.
For flat putts use the same formula but subtract 30%.
For downhill putts subtract 35%.
This won't always get you there, but it will get you closer. Keep practicing and take notes to refer back to for future putt situations.
Best of luck.