I found this great article in Real Simple magazine that talks about how to look great in every photo. And here's some tips:
Problem: Exaggerated Facial Features
Solution: Turn your head. Most people have asymmetrical features (for example, one eye is larger than the other or the right ear is a bit higher than the left). That way, facial asymmetry is not as obvious. This particular angle also has a slimming effect, as it draws the eye up and down (forehead to chin), not left to right (eye to eye).
Problem: Deer-in-the-Headlights Look
Solution: Don’t look straight into the lens. “Focus your eyes just above the lens instead of staring directly into the camera,” says Patrick McMullen, a celebrity photographer and author. “I usually look past the lens, over the photographer’s shoulder,” says Miss America runner-up Jennifer Dupont. “And show some personality. Sometimes all it takes is the slight raise of an eyebrow.”
Problem: Fake Smile
Solution: Don’t say “cheese,” which usually conjures an artificial smile. Instead, ask the photographer to throw out an unexpected word, like “money.” This will usually elicit a genuine laugh, and your expression won’t look forced.