When you go to custom car shows to take photos, if you want to get the right shots with the best light you have to go very early and stay late. The best light is early morning and just before sunset. Always take a good external bounce flash to eliminate shadows and the best camera you can afford. If you can you should also take a table top tripod (for use on the floor for low shots) and a mono-pod.
When shooting cars get the details, whether it's a tall tail fin side shot or a hood ornament. You may even want to lay on the ground to get the supper low angles. To get ideas I look at car magazines to see what angles they use. Always shoot with the sun at your back. If the car's hood or doors are open the car owners usually will close them for you to shoot their car--most car owners like to have people photograph their cars.
As most photographers will tell you, you can't take too many photos, and with digital that's not a problem. You won't know until you download the photos which ones will be useful. At a good sized car show I take three to four hundred photos. I may only use one fourth, if that many. I don't stop shooting until I get back to my car. I try to take at least six or seven shots of each car that interests me.
Experiment with your camera's settings and have fun with it!
