1. Watch the BackgroundYou've probably heard this idea a lot but its always true. Watch your background! No one looks good in a tux with a full garbage can behind them or an advertisement-littered telephone pole growing out of their head. Pick a spot where there is a relatively "clean" background or at least one that fits in with the idea of prom. Some ideas are a few feet in front of a shrub wall (blurs to make a nice green background), in front of the limo, on a staircase, and in front of a blank wall.
2. LightLight is your next biggest concern for fabulous prom photos. Find a spot where the light is relatively bright but no one is squinting (a shady area outside can work well). Check your camera menu for a feature called something similar to "force flash", "flash always on", or "fill flash" to activate the flash even though the camera thinks there is enough light. Tape a small piece of wax paper over the flash to diffuse it and the fill flash will create a pleasant light to the face even when in shade.
3. Watch for ShadowsShadows thrown across faces at odd angles can turn a great photo into a ghastly disaster. As mentioned in the light tip please be sure to diffuse your flash in addition to paying attention to shadows that may be on the face and change location if necessary to remove those harsh shadows.
4. Let the Couple Get Close to Each OtherLet the happy couple get close to each other in the photo. Cheeks touching or a hug add a lot to a prom image. Think about the formal prom photos you've seen in the past and let the couple pose similarly.
5. Getting "The Pose"How you pose in a prom photo can make a lot of difference in the finished product. Never let yourself be photographed straight on in a full body composition. The flattening effect of photography will add the illusion of being larger than you are. Face 90 degrees away from the camera and then turn 45 degrees back towards the camera with your upper body. Finish by turning the rest of the way towards the camera with just your head. Also, never tuck your head back or you will have a double chin in the photos. Move your head forward a bit to elongate your neck. Photography poses rarely look normal except through the lens. Our About.com Beauty Guide has some excellent advice for appearing thinner in images.
6. Use the Program or Action Setting on Your Camera
If you do not use the manual setting on your camera then use the program setting with shutter speed set for at least 1/150 of a second. If your camera does not have a program setting use the action setting. I know this goes against the "use the portrait setting" advice you've heard a dozen times but there is a good reason for this. The portrait setting uses a slower film speed and wider aperture to blur the background and gain a more fine grain texture. This creates a very tiny depth of field on some cameras (sometimes so small the nose is in focus and the eyes are out of focus) and results in a slow shutter speed that can lead to a shaky image. Using action mode is a good compromise of aperture and shutter speed.
7. Get "The Smile"
Nothing ruins a photo faster than a forced fake smile. As the photographer, part of your "job" is to capture a genuine expression. Try saying something completely ridiculous instead of "say cheese". Try something like "say purple people eater" and watch. There will be a moment of complete confusion followed by a laugh. In the middle of all that expression change will be a beautiful smile - be ready to click fast when it appears.