Body Language
Body language is usually entirely subconscious, but with a little bit of effort you can work to make your body language say what you want and learn to read the body language of others.
The primary goal behind altering your own body language and paying attention your opponent’s body language is to help develop a rapport with them. You want the other person to like you a bit more so they will offer you a better deal or concede more than they otherwise would. The goal, however, is not to necessarily become friends with them, since this is still a business transaction.