As a former professional photographer, I have three pieces of advice...
The first, which SHOULD be obvious, is to hold the camera HORIZONTALLY.
Cars are neither people or five-story buildings. Look at the car ads on Craigslist and see how common this mistake is.
Second, lens focal-length DOES make a difference. Wide-angle can distort perspective while longer lenses can flatten it, (a GOOD thing for most exterior shots.) Wide-angle lenses are most useful for car interiors and engines.
Finally, a cloudy, overcast day gives the BEST, most even and soft lighting.
Just try to keep the sky itself out of the picture, (have a background of trees, an attractive building, etc.)
P.S.- DIGITAL zooming lowers resolution; OPTICAL does not.
