Facial expressions are the toughest aspect of a photo shoot to master. I always suggest that you practice in a mirror before a shoot. Even though you feel totally silly, this is the best way to see how your expression will read in a photo. I recently came across an article in Glamour Magazine's September 2009 issue about how emotions affect our look. The photos that accompany the article really showed a range of facial expressions that are a great reference for preparing for your shoot. Here is a link to the article, and I highly suggest grabbing a copy of the mag! Eva Mendes Shows Us How Emotions Affect Our Looks Beauty: glamour.com.