Green reading is largely a matter of experience and judgment. The more practice you get, the better. That said, playing on greens you are unfamiliar with can make it a tough assignment. The best advice I can offer is this: Don’t wait until you are on the green to begin reading it. From fifty yards out you can observe a great deal about where water would drain to, thus the break, that you cannot see while standing on the putting surface. And double check your read by plumb bobbing. You can disregard the theory behind it and just recognize that gravity will make the shaft pretty much vertical, helping you avoid being deceived by the surroundings as to what vertical, and therefore flat, really are.