I found this one which is preatty good and professional and the author also wrote an interesting and complete article about tips on sketching cars correctly on paper.
His principle is to abandon for a while all that computer digital drawing stuff and be concentrate on a real hand made car sketch on white paper, you know me now I totally agree on that!
So I invite you to read the article and tips and see also the tutorial video he posted.
Click : How to sketch a car on paper!
