1. Unless you are freakishly symmetrical—in which case you are probably an android and have better things to do than pose for photos, like plot the downfall of your human masters—you have a good side and a less-good side. Figure out which one is which and position yourself accordingly.
2. Angles are your friend. Angle your body three-quarters toward the camera rather than straight on, with one foot slightly in front of the other. Put your weight on the back foot.
3. Hold your arms slightly away from your body so that the upper part doesn't appear flattened and, hence, wider.
4. Push your chin out a little and make sure you're not being shot from below to avoid a double chin. I've also heard that sticking the tip of your tongue right behind your front teeth helps.
4. Mom was right—stand up straight!
5. Relax. You don't have to look like a model in casual shots. When you're dead and gone, no one is going to look at your photo and say, "Jeez, what a horrible picture of cousin Rita." OK, someone might, but the important part is that they will remember all the good times with you.
6. If all else fails, blame the photographer.