It is funny you should ask me this................................... I have recieved some tips from Jeff @ Immaculate when he did some cars with me as far as manual settings and what not, also tips from Daniel @ Car Connoisseur where I have played around with shutter speed/iso/lenses. Lighting is very important too, but I do not spend a really long time on pics as I am in production and need to complete vehicles in a timely manner.
I also have two different cameras a DSLR Nikon D3000 which Lucci sold me for the cheapness, and a point and shoot Canon Powershot which has a 2.8 lens that really takes nice pics to pick up defects in the finish where a DSLR cannot do sometimes unless the lighting is optimal.
try not using that flash right on your camera - have plenty of other light from all directions that should help a bit if you dont want to get into it too deep...