1) Experiment with Different Angles
Holding the camera below your face will only accentuate your chin and nose (not always the most flattering). Try holding the camera slightly above eye level for a shot that flatters your features. Remember to hold the camera as far away as possible too.
2) Try Tilting Your Head
We all have a "best side." Try tilting your head in different directions to find the angle that best highlights your cheekbones and accentuates your eyes.
3)Use the Rule of 1/3's
Photographers all know to align your subject in the left 1/3 or right 1/3 of the picture. When we take selfies we tend to scrap that rule and try to center ourselves. Your picture will be more interesting if you can position yourself slightly to one side.
4) Stick Your Neck Out
It may seem awkward, but nobody wants a double chin in their selfie. Try extending your neck out slightly. The effect will be to elongate your neck and accentuate your jawline.