Recently finished an interesting book by Michael Fleishman Starting Your Career as a Freelance Illustrator or Graphic Designer. I found it to be a comprehensive source of information for anyone, who wants to enter the world of freelance graphic art. There are chapters covering the topics from making up your mind about freelancing to organizing your own studio.
Personally I liked the descriptions of different markets, where an illustrator and graphic designer may find projects and clients, for example the magazine market, book publishers, advertising agencies, etc. I also found a chapter with different forms and templates for managing your business very interesting.
This book is definitely a nice read.