You really need view some tut's but it's not bad-

frnt rim is off and you shouldnt used the lensflare to turn on the lioghts and it would have been cooler if you havent turned them on at all:P but just keep it up:-d

It's not bad, but there are some points:

- The color looks too saturated
- the black parts (hood & roof) are a bit too grey, you could try darken them
- wheels are good, but the rear is off
- The front bumper needs more depth, you could try to add some shadow
- skirt is good, but the exhausts in it have the wron perspective
- the side mirrors look strange

if you can fix those things, it would look way better!
it may be a long list, but it's all ment well.

I think you should try first some smaller things (like lowering, changing rims...), and if that's no problem, you should try more difficult things.
That's just my opinion, you can do whatever you want to