I agree reading special literature won't do much good.
Probably staying calm & self-confident might be the best solution.

Say good-bye to your scaredy-cat self!

Body language is of real use, but only when you're an expert in it. It's very difficult to control your body language because it's our subconsciousness that is responsible for it. Knowing the basics won't help you. You should read a lot and practice a lot to make your body language work for you.