Try to think about something that makes you happy when you get your picture taken. Don’t look directly at the camera - somewhere in the general area will suffice and keep you from feeling as overwhelmed. Don’t square up to the camera. Instead, turn your body on a slight angle and turn your head in the general direction of the camera. You don’t need to break out into a full-blown smile - try for a grin with your lips barely parted. Keep your elbows out away from your body, but not so much that you look like a chicken. If you have pockets in your pants, put about half your hand in the pocket facing the camera. Finally, take a deep breath and relax to avoid looking stiff.

Hope this helps!