I stumbled across this very informative tips for freelance illustrators blog post by illustrator Nate Williams. He gives a nice overview of the process he uses not only on the business side of things, but also on the creative side.
The advice is a bit heavy on the website aspect (with which I totally agree), and quite detailed, but some of the other advice such as creating a postcard and sending it out to your mailing list is a bit vague in regards to best practices in creating a mailing list, and the best way to design that postcard – in the sense of how to present your work to art directors in a direct mailing piece.
Good website construction and knowledge of the SEO (Search Engine Optimization) behind the code is excellent advice, but I think the next step is to send out mailers to the potential clients that might not search for illustrators online. Art directors are inundated with promotional mailers on a daily basis, and may not even need to go out and do a Google search to find new talent.
Williams also has some great explanations of how to keep projects on track (again web-heavy solutions), as well as general tips on attitude and expectations. Worth a look.