I really love the illustrator Brandon Ragnar Johnson (http://www.ragnarama.com/). He's got a great, really simple, really elegant style. As a result, it's REALLY hard to draw similarly. When I've tried to copy his work for practice, I fail miserably. It's such a simple line that you can't hide behind it... it's either right or it's not. So before tonight's Steelers game (can't draw DURING the game - that would be ugly) I copied some faces out of a book of his work that I have.
Again, you can learn a lot by copying other artists' work. By no means am I passing this off as my own - it's 100% copied out of a book.