i used picture it 10

before

after

Is this your first attempt? If so, you haven't done a bad job. A few points to pick out. Where you have made the wheels black with an overlay? you have caused the whites to blow on the rear. If you make them dark grey first then make them black from there then that shouldn't happen too badly. The front grille is way to black against the car, once again use the same method as the wheels. For the bumper... if you make the mesh larger than the bumper and slowly brush it out with a low oppacity brush it should blend nicer. On the lights it looks like you have used a brush on it? If you make a path, fill it in black then lowe the oppacity it will look smoother. Either way, just a few tips of advice to think about.