Or do you slouch, perhaps with your shoulders drooping, your head forward and your stomach protruding? Are you saying to people that you are not sure of yourself, are not poised and, therefore, not the one they should seek out and get to know? You may be turning people away without even being aware of it.
Command respect by standing tall and claiming the space to which you are entitled. Plant your feet about six to eight inches apart with one slightly in front of the others. My workshop attendees always remark about how this positioning makes them feel "grounded," "rooted" and "balanced" ... great ways to start any encounter!
You also tell people through your posture if you are want others to approach you. For instance, if you are talking with one other person and the two of you are forming a rectangle, you will give the message that you have "closed off" your space and don't want to be interrupted. If you doubt me, stand by two people who are in the rectangular position and see how long you go unacknowledged. The two will see you out of their peripheral vision, but won't include you until they have finished their "private" conversation. If, on the other hand, the two of you stand with your feet pointed outward like two sides of an incomplete triangle, you will be inviting others into the conversation. You can make that all-important eye contact.