Try shooting cars during cloudy or overcast days for the best results. I like white cars at night under street lights as it's hard to see the lines or any depth on white cars during the day). Use a tripod when you can for sharper images and try using a polarizing filter to help with reflections in glass.
For general photography, there are tons of sites with tips and tutorials. I would browse each site listed under the Photography Tutorials section on
http://www.lightstalking.com/photography-websites. I highly advise
http://www.cambridgeincolour.com and
http://digital-photography-school.com/tips (especially the tips for beginners articles). But most of all, get out of auto mode and TAKE A CRAP LOAD OF PHOTOS. Start shooting in Aperture mode and play with depth-of-field.