"I'm a storyboard artist. When I couldn't find a good book on drawing folds, I decided to analyze folds myself, and I'm sharing what I've learned. Well drawn folds in clothing can help make a drawing look dynamic and alive. But usually folds just seem lumpy and unconvincing--especially when drawing from your imagination.Kelly's guide is unlike anything else I've seen on the subject of folds. After 20 pages of demonstrating how folds are formed, Kelly includes a chapter on how to draw folds in people's hands and skin. The last six pages deal with the way clothing is tailored to deal with the range of human motion. VERY interesting stuff!
The reason clothing is usually badly drawn is that you can't draw folds unless you understand them.
In this document I’ll explain why folds look and behave the way they do. The information in this document will help you get started learning how to create convincing-looking folds from your imagination, so you’re not limited to drawing only what you see in front of you. "
The tone of the writing is very conversational and the drawings are lively and clear.
How to UNDERSTAND FOLDS and DRAW CLOTHING!
Since we're on the topic of how to draw clothing and folds, here are a couple links from Mark Kennedy's Seven Camels blog to some fantastically helpful scans from the Famous Artists Course chapter on how to draw folds and clothing:
UPDATE #1: Walt Stanchfield PDF on "A Simple Approach to Drapery"
UPDATE#2 Famous Artists CARTOONING Course Lesson on How To Draw Clothing and Folds
18 pages of high-resolution scans from the long-lost Famous Artists Cartoon Course courtesy of CartoonCrazys