Oh, don't get me started on the "rule of thirds", I don't like it.
Gimme the golden ratio any day! Anyway, I'm not a big believe in rules - hence, using things like fisheyes and LensBabys. Honestly, I just like Bryan Peterson's way of thinking of it - the farther to the edge the focal point is, the more interesting, but the more it needs to justify being there. Different subjects should be composed differently.
I think you can
get a good photo at a car show - but it's not all that easy. You won't get the glamour shots that VisualEchos does - they're beautiful but frankly I don't have the patience!
But you can certainly get nice detail photos, and if it's not too crowded, you can get farther away and use a telephoto to isolate a car from anything around it. It's good IMHO to get low, too, which the telephoto helps with. For example:
You can also capture just part of a car. A short depth of field is definitely your friend. This was at the last LOG, shot with a lens that was built sometime around 1960:
If you want really short DoF, you need a fast prime. Here's a shot at F1.2, 50mm from a LOONY breakfast gathering.
Or, just look for some interesting part of the car and focus on that:
Everyone has their own style and ultimately, if you're not trying to sell your photos, the only person you have to please is yourself.