Our body language can communicate a lot about how we relate to people. Often our body language is unconscious, but when on the negotiation stage, mindfulness is essential. There are excellent studies and helpful books on this topic[i]. Agreements are reached more often with positive body language (leaning forward, smiling, mirroring, head nodding, open posture) than closed body language. Disjointed or unusual body language can frustrate a negotiation.
An example is a stress response such as self-soothing—rubbing your own hand, hair, face, or leg is a soothing response. This is an indication of anxiety, as it is assumed the person is conducting self-care to soothe the anxiety. Mirroring, or doing what the person across the table is doing, is also calming to them. Using the same tone of voice on a phone call is also a cue to mirror and match tone and volume; however, do not mirror stress calls, you may match to form a boundary, then de-escalate in tone and volume.
Filter your visual input, and focus on the substance of the negotiation. Be aware of your tells and arrest nervous habits. In any relationship where there is loss or gain to be divided, less information is more. Don’t let your body speak your thoughts. This requires detailed study and homework.