I'm gonna beat Bignose here with this advice.

Try the ladder drill ...

Go to a practice green and place a tee every 3 ft from say 10-40 ft away. The goal is to lag the putt between 2 tees. Start with the short ones, and move up one each time. Then start picking random targets. If you can get to the point that you can almost always leave the ball between the 2 tees you choose, then you will have your distance control down to leaving a 1.5 ft putt (the hole being between the 2 tees).

Do it flat, downhill, and uphill.

One thing that helps me, but I know a lot of people don't like thinking of putting this way, is to aim for a target assuming a flat putt. So if I have a downhill 30 footer, I might visualize hitting to a point 20 ft away, adjusting for the slope. When I putt, I pick a spot that takes into account speed and break, and then just think of a flat putt to that spot.