This might be a bit old school for some of you as this was posted on a bunch of sites a few months ago. But I recently was going through some of my bookmarks and reread the article and I believe the information is extremely valuable.
Dave Roman is an amazingly talented artist who's work has appeared in such books as
Flight,
Agnes Quill, and
Nickelodeon Magazine. Dave is also the associate editor, comics associate, and a writer for Nickelodeon Magazine. So in short, he has had more then a bit of experience in the illustration work and he knows his stuff.
The article itself is quite long and detailed but every word in the article is pure gold. Dave covers everything from portfolios to how to work with an art director, from media recommendations to how to advertise yourself online, and everything in between. And unlike many books out there which are years old, technophobic, or written from "old man" perspective/about the industry years ago, but Dave's article is about as current and relevant as possible.
So if you have a moment of free time then go and read the article. If you're busy at the moment then bookmark it and go back to it once you are free.
http://www.yaytime.com/guide_freelance.html