Selfies, unfortunately, have become a fact of life. Everywhere you go now you will see people standing in front of every icon in the world holding out a camera or a phone and taking their own photograph. I would prefer not to, however my wife is a huge, huge, huge fan. First rule for taking a selfie is, and I cannot say this with enough emphasis, no duck lips. Duck lips are an absolute no-no. Be yourself, be natural because at the end of the day the photograph will turn out better. The person in the photograph with the longest arms needs to be the one holding the camera.
If you're using a phone, make sure you know the phone's operation pretty well so you can take a photo extremely quickly. Secondly, look at the head positions. My head is almost straight on at the camera, whereas my wife Nicole, her head is leaning towards me and a little bit down. That way we're not seeing any horrible double chins or anything like that on a female. We always want the head sort of just down, just a touch. But generally for the men, eye-level. None of these up high things.