Americans like to look at the other person in the eyes when they are talking. If you don't do so, it means you are unhappy, or are not interested.
For Americans, thumbs up means yes, very good or well done; thumbs down means the opposite. To call a waiter, people put one hand above the head. It is all right to point at things but not at people with the hand and index finger. Americans shake their index finger at children when they scold them and touch them on the heads when they admire them.
Learning body language is sometimes difficult. If you don't know what to do, the best thing to do is smile.
