I totally feel your pain. This is a little trick I tried out before my last convention:
Stand in front of a mirror and experiment with your facial expressions a bit. If you want a smile, try a few different ways: a grin, a smirk, etc. Find one you like, then try to remember how it felt when you were expressing it on your face. That way, when you're getting photographed you can achieve the smile you got in front of the mirror by remembering how it felt on your face. It may sound strange, but it does work after a few tries. Not sure if I explained it well enough...
Hope that helps! Have a good time at the photshoot.
Last edited by Tealeafy : 04-19-2011 at 08:07 PM.