Get above, and try and avoid really wide angle lenses if you can, the perspective distortion usually makes cars just look wrong, especially if they're low and sleek. If going low down. get below ground level if you can, that can work quite well, as like getting above, it's not a view we're used to seeing so can look more interesting.
Car shoot bingo:
Light painted overlooking a city
In a Multistory car park
On an industrial Estate, bonus points for being in front of a roller shutter door
Rig Shot
Long Exposure whilst moving from inside shot
Inside a Tunnel
Off camera flash lighting only car against a seemingly black backdrop