I'm far from any kind of expert, but here are some tips that I have found useful!
Take pictures on a cloudy day (lighting is everything)
Avoid distracting backgrounds (trees, people, other cars, poles)
Watch out for reflections (don't go
overboard on the waxing)
For auto portraits, try to take the picture at car-level, not human level.
Experiment with creativity! (And remember what
works)
Any one else got any tips?