1/13 Avoid a Double Chin
No matter how thin you are, you can end up looking like you have a double chin in a photo. The trick is to pay attention to the camera position. If the lens is at eye level or above, you're in the right frame. If the lens is below your eye level, there's a good chance the image will come out looking as if you have an extra chin.
Bend your knees a bit so you're at least on an even plane with the photographer, if it's not a full body picture. If you're quite a bit taller than the photographer, sit in a chair and look up toward the camera. Be sure to project your chin out an inch or so more than you normally would. You may feel a bit awkward, but you'll be much happier with the photo in the end.