When posing you can keep good posture (unless the photographer instructs you to do otherwise) by holding your stomach in to give your abdomen a more toned appearance and keeping your shoulders back, but relaxed. If you are worried about your face appearing heavy, just bring your chin forward a little to avoid the appearance of a double chin in your photos. (Try that in the mirror and you'll see what I mean...) Keep your fingers slightly apart and pointed away from the lens. Let your hands fall naturally into position whenever possible. Remember your nail polish, ladies! A good photographer will remind you to do this during your session, too.