it isn't easy as u think
u need to make several things to be good
try this one as first http://www.dmmultimedia.com/3dtips_03.htm
if u can't do it, u need to get much experience
I like your car dude but, the bumper, when you were making it, you sent me a pic and i saw where were you modifying, so, where you modifyied, i can see one "line", i think you need to attach this bumper with the XRT and after, at vertex menu, use "target weld", then it will be perfect.
1st- Its nice
2nd- Where are your brakes? And I think you could give a better material than this one
3rd-I think you could give a better material than this one too, and the guy's arm seems crazy.