Pic 4 has the best lighting (just needs to be cropped differently) and pic 5 is getting closer to a good composition. Image quality looks good (except the one where the focus is on the timber pallets not the car! You need an epicly low aperture for that to look artistic!), but overall not bad for a first go!
Things to think about with each shot:
- where's the light coming from?
- where's the main subject (usually the car) in the shot - should be positioned according to the rule of thirds
- what angle are you looking at the car from? IMO the most boring shots are front/rear 3/4 photos shot from standing height (as it's the same view you always look at cars from with your eyes!) Get low or high for something a bit different.
But mostly, practice, practice, practice! Like the giraffe, I'm a complete novice and only offer advice from my own self-taught experience - been shooting cars for about 4 years, just for fun (as I'm out driving them anyway!) but I think my technique and ability has evolved and improved. You can check out my progress here:
http://www.flickr.com/photos/walkie86/sets/?&page=1