Many of the students that come to our Frankly Golf Putting Academy in Orlando report that they have difficulty reading greens.
A quick tip to help you understand more about the slopes on the green is to “feel” the slopes with your feet, as well as reading them with your eyes.
So next time you play and are walking around the line of your putt, try to feel the slopes under your feet and use this information (in combination with what you see) to make a decision on the break and pace of your putt. You will be amazed how much this can help!
franklygolf 
Seems to me that if you can’t get a read on the slope with your eyes, then the slope is so slight that you would never get a “read: with your feet.
True. I play with a gentelman now 80 years old and an excellent putter. He says when in doubt aim for the center of the cup with decent pace.
The best way to improve green reading is to get “The Fundamentals of Putting.” It has the BEST description of fall-line reading that I have ever seen. (Totally unsolicited from a big fan.)