One of the most difficult aspects of golf is learning how to read a green. The trick is to stick to a few proven rules and the art of green reading will suddenly become less of a mystery.
Find The Highest Point of The Green
The first thing you need to do when you read a green is to find it's highest point. One you have done this try to imagine a bucket of water falling on that spot and picture in your head where the water flows. Doing this will give you a great idea of how the ball will move on the surface and it will help you in judging how hard you need putt because you can judge uphill and downhill easily.
If you are not playing in a tournament you can try pouring water on the green for real and testing the technique in action. It's important to remember that doing something like this is highly illegal in actual tournament play.
Walk Around The Green
Walk around the green and feel the ground underneath you. This technique is even more helpful if you do it with your eyes closed because you have to depend on your sense of touch only and you will visualize which way the ground is sloping.
Try Looking at the Putt From a Different Perspective
There has been lots of times where just looking at the green from a different point has given me a clearer indication of the slopes or hills. Even if you don't think it is necessary try it and you might be surprised to see you have missed something important.
Look at the Horizon
When you are judging a green look to the horizon and compare the lie of the green to it. On some courses with a lot of elevation this will be impossible, but if you are playing somewhere where you can find the horizon it can be a big help. Try to remember that if there is a large body of water nearby like the ocean or a lake then the green will probably fall towards it.
Try putting some of these golf tips into practice and you will notice a marked improvement in your short game.