This article reports on the persuasiveness of simple mimicry; if you mimic another individual's nonverbal behavior, you're likely to be more persuasive than if you didn't mimic. In addition, mimicry seems to increase pro-social behavior even for those not involved in the mimicry interaction; that is, if someone mimics you, you're more likely to engage in some pro-social behavior. As you can imagine, an understanding of mimicry can be useful for the person attempting to persuade as well as for the critical listener. And, of course, recognize that mimicry when taken to the extreme can backfire and be perceived as insulting. There's a great deal of research on this; just search for "mimicry" or "behavioral contagion" or "communication accommodation."