How do you read the green?
Reading the green is what determines the intended aim and speed of your putt. You can have the best putting stroke in the world but if you can't imagine how the ground affects the roll of your ball, it will be difficult to make putts.
To read the green, first observe the general slope of the ground as you approach the green. Next, get more specific by bending down a few yards behind your ball, in line with the hole. Scan your eyes left and right. Is there any unlevel ground? As you walk around, feel and observe the ground. Look from the other side of the hole for a different perspective. Observe your putt from the sideview to see if your putt is uphill or downhill.
Reading the green does not take up much of the group's time if you make it your main focus to study the ground from the time you start walking on the green until it's your turn to putt. Use your time wisely. When your playing partners are putting, stand out of the way and observe at least one of the views stated above. There really is no place you can't read the green from. Watch the roll of the ball from others that putt before you. Secretly read their putt and see if the roll of their ball is what you expected. Pay even more attention if a player is putting on a similar line to your putt.
Bob gives a great hint when he says that unlevel ground will affect your ball more as your ball slows down near the hole. Watch as your ball nears the hole. The more you observe putts, the better your imagination becomes. Even if your putt misses, you learned something if you observed the roll.
There are two benefits to observing the ground intently with your eyes. First, you will become a good green reader, and second, using your eyes more intensely keeps you more focused and present. Both will help you play better and enjoy the game more.