this is a great tutorial because it shows exactly the fondamentals of car design sketching. 8 steps to go from a linework to final color sketch, the author of this demo is designer Jhon Frye Art Center College of Design alumni.
Believe me it is important to learn to do this because it is going to be the same type of method to follow when you pass to Photoshop digital technique. This is the basics of car drawing after you learn this you can personalize very easly the technique, so click Jhon Frye tutorial and check all 8 images and written comments to explaine each step.
It is really well done click and enjoy.