Discuss how facial expressions and other body movements influence the meaning of a hand gesture. Discuss body language in a bar or club. Consider such factors as personal space, posture, eye contact, speed and angle of movement. For example, if you place a coin in one hand behind your back and then present your fists to a body-savvy person, that person may be able to detect where the coin is. Have students form pairs to try this coin experiment.
Some people are much more adept at it than others.
If you're good at it yourself, demonstrate with a volunteer in front of the class. Have students pair off. The task for the other student is to follow or mimic everything that the leader does. Encourage people to use both obvious and subtle behaviors. Do this for a minute or two, then switch roles of who is leading and who is following.