Lean Forward

No, itīs not because you want to show off your cleavage. Itīs because you want the guy to know you are interested in him! If you sit up straight or lean back, you give off the impression that you are not interested in the guy, and want to be away from them. By leaning forward, towards them, you show your interest in him.

By the same token, don't cross your arms. That is a very defensive posture. Keep your arms open.