Aside from the occasional curious client, I believe it's usually other illustrators that scope out illustrator blogs. Considering that, I've decided to post some freelancing advice that I've passed on from time to time. I'm passionate about the topic of freelance illustration, and am happy to discuss my experiences, when asked. In that vein, I'm going to begin a series of writings on the topic, and I invite your feedback!
Without further ado...
Get Used to Criticism.
Prepare to have your artwork verbally ripped to shreds after pouring hours of blood, sweat and coffee into it. Nothing is beyond reproach, and you need to develop a thick skin. If you see any illustration as "your baby" then you'll come to dread dealing with clients.
Furthermore, if it makes you uncomfortable receiving criticism and direction, the art director will sense it. An awkward or difficult exchange won't make them want to work with you again.
Refine your portfolio, put it online. Refine some more.
Display the kind of work you want to do, not necessarily the type of work you are getting. It's difficult to establish your style, and sometimes you need to take the jobs that are willing to pay, especially when you're starting out. That doesn't mean that work should go in your portfolio. Dress the part. Don't include work that doesn't reflect the projects you want. Student assignments often (but not always) looks like student assignments. Don't include pencil drawings of your cat/dog. You might be thinking, "This shows that I am multi-talented, and can handle styles of many varieties and difficulty" - but it sends the incorrect message that you are seeking pencil-drawing, animal subject-matter assignments.
The printed portfolio is still relevant, but I believe it is dying. Creating a user-friendly, simple website portfolio is essential to reaching art directors that don't have more than a few moments to look at your work. Keep it simple and easy to navigate. Overblown, high-concept Flash sites are often confusing, and can take forever to load.