Why do car selfies look so good?
Natural light is preferable and window lighting is best because the light is filtered. That's why selfies you take in the car generally look better than those under fluorescent lights.
Where do you hold your phone when taking a selfie?
Hold the camera at eye level rather than above your head so that you don't look squashed, like you're too low down or have a double chin. Look into the lens straight on to avoid shifty eyes.