Your body language, eye contact, hand gestures, and tone all color the message you are trying to convey. A relaxed, open stance (arms open, legs relaxed), and a friendly tone will make you appear approachable and will encourage others to speak openly with you.
Eye contact is also important; you want to look the person in the eye to demonstrate that you are focused on the person and the conversation (however, be sure not to stare at the person, which can make him or her uncomfortable).
Also, pay attention to other people's nonverbal signals while you are talking.
Often, nonverbal signals convey how a person is really feeling. For example, if the person is not looking you in the eye, he or she might be uncomfortable or hiding the truth.