I use same method as gwlee27. As I approach green I always look for the direction the water is to drain off the green. All greens need to drain.Thats your predominate break and slope. I then like to walk parallel to the path feeling the break with my feet. Reinforces what I see. Get behind for final read. The rest is trust. My most common error is to read some break when there is none. In those cases when I not sure especially uphill I'm firm with the putt.
Most exasperating part of putting is footprints 1-2 feet around the hole on soft greens. Was out at Lake Arrowhead today after rain (Sunday)and they were there. As the ball slows down they really can bounce a ball around. Did roll in a 15 foot downhill breaker for eagle on the 12th hole on Lakes course.
Sometimes its better to be lucky than good.