Illustration is a tough business, and I can't imagine how I would have made it without the Guild. Through this organizationwhich is made up almost entirely of professionals in the field who donate their timeI've learned how to prepare a solid contract and how to price my work fairly and competitively. Plus, the people I've met through the Guild are some of the nicest people I know.

Starting
Your Career as a Freelance Illustrator or Graphic Designer
Michael Fleishman's book is the best introduction to the world of freelancing that I know. Every aspiring (and established) commercial artist should read this cover to cover. It's full of great, practical advice, and the first edition was what got me started in the field over a decade ago. Highly recommended!

http://www.illustrationclass.com/
Here's a great resource for illustrators of all stripes. Von Glitschka, a designer and art director, has put together a great collection of illustration tutorials, complete with sample files to download. He also has a nice section of "Creative Exercises" perfect for getting the mind going when it's stuck in the virtual mud. Von clearly puts a lot of care into his site, and there's something there for everyone.