I discovered this today. It's a 3 part article on how to do illustration, but a lot of the tips can be very useful not just for that but also for puppet designs.
http://www.smashingmagazine.com/2010/06/10/the-process-behind-good-illustration-part-1/
http://www.smashingmagazine.com/2010/06/17/the-process-behind-good-illustration-part-2/
http://www.smashingmagazine.com/2010/06/24/the-process-behind-good-illustration-part-3/

This is a great article!

Yep - have actually put a lot of it to use already. The bit about making your designs larger than what you need them to be has really helped me a lot with some web design graphics I've been working on. Seems so obvious now, but I never thought of doing that before and it's been a lifesaver in trying different elements at different sizes to get it to look just right. This will be so handy also for puppet patterns when I usually try working at a size I think is useful, and then end up needing to redo the outline because I've needed to enlarge it later.

Good article Na.