I find that body language books, although they can explain how to read other's body language, they can be confusing as its just theory, especially if you don't find it easy to visualise what is said as body language is a visual thing.
The best thing to do in all honesty is get a friend or relative to guide you through it if you become confused. I actually have a friend who is excellent at reading body language and he helps me with my body language skills. I'm now a lot better at it, but was also gradually taught by my parents. If you know someone like that who understands your predicament then I'm sure they won't mind trying to explain it to you as it can be much better in practice than in words.