Instructions
Be aware of lighting. Very few people look good in fluorescent lighting. Find a soft natural light that won't create too many shadows on your face.
Place yourself at an angle. Avoid facing the camera head on. If you are at an angle you will look taller &thinner.
Position yourself so you are looking up at the camera. This is also a great way to fix those times when you have to take a photo of yourself for a profile picture or if no one is around. This way your eyes will look bigger &they will be the focus of the photo.
Take a lot of photographs. Instead of pinning all of your hopes on just one shot, take dozens of pictures. This increases the odds that one of them will be really good.
Use a relaxed posture but don't slouch.
Have fun. Have you ever noticed that some of the best photographs are when you are sticking out your tongue or wearing a funny hat? If you are laughing or are genuinely happy it will show through.
If you are nervous in front of the camera, have a friend take candid shots of you throughout the night when you aren't paying attention.