I have a business plan I wrote for my freelance business in a class in 2006. I just spent the last couple hours revising it, since I have a much better idea of what I can do and just how to do it now.
I'm adding in sections specific to my comics, because to have that nailed down in such an official way would probably help me lots. I already have things like promo materials for my comics, taglines, elevator pitches, etc... They're just not organized in a formal document like the rest of my business stuff. Now's the time!