A really good picture is less about reality, and more about knowing how to position yourself for the camera. it’s key to avoid direct head-on shots.

Position your body 45 degrees and put the arm closest to the camera on your hip. If you’re being shot head-on cross your legs.

Smiling is a tricky thing, but you need to do it naturally. Too wide smile will make the picture really bad. 

And now some really good examples: