I did this one in marker so you can see every single line. Ideally you would want to start the sketch lightly and then build the line thickness up towards the end with a ballpoint pen or fine-liner.
Thumbnail sketching. It's easy to do profiles and in most cases is more helpful in the ideation stage, but what do you do when you want to show a detail you can't show in a profile sketch? This video shows the same steps in three similar car designs. Once you master these simple steps then you can fill up a page of cars like I did with this:
^that was just a page of 8.5 by 11 paper that I took into photoshop and assigned a gradient to. It was featured online for one day on the front page of Core77 Design Magazine.