If you have even a slight double chin never take the photo from underneath your face. Here is a perfect example:
A seemingly universally flattering angle is slightly above and having your face turned at an angle. A full on face shot makes for a round face. It's usually more flattering to turn to a slight angle. Learn how your face looks from a profile to a full face shot and all the angles in between. A good standard angle is a 3/4 shot, with both eyes visible to the camera. If your eyes are different sizes you can minimize the difference by turning the larger eye away from the camera in a 3/4 profile, this will mean the smaller eye appears larger because it's closer to the camera, and the discrepancy will even out.
Women: wear make-up. Even a little foundation will help even out your complexion. Men: shave. Or at least trim your eyebrows & stray nostril hairs. (I think this is a good rule of thumb even when NOT having your picture taken)
Look slightly above the camera — apparently Jacqueline Kennedy Onassis did this. Wait just a minute - who could see where she was looking anyway with those big huge sunglasses on? Unfortunately, you can't wear shades and scarves 24/7, especially if you're running for president.Don't be afraid to smile once in a while but remember that smiles cause lines on the face. A relaxed face with no smile or a very small quirk of the lip combined with alert and sparkling eyes can convey as much emotion as a full bore smile.
Most importantly, I found this gem while doing my research: When you point your toes all sorts of good things happen (???), your legs get longer (!!!), your calves get shapely, and if you're on the balls of your feet your posture gets better. You should always be aware of good posture. If you aren't wearing high heels, pretend you are by pointing your toes. (I am wondering if I have to do this all the time, or just when getting my picture taken?)
Today's Chinese Proverb: "I hear, I forget. I see, I remember. I do, I understand. (p.512)