As of this month, I've been working full-time as an illustrator for eight years. I went back today and read what I'd written about freelancing five years ago. I think it still holds up as advice, especially for newer illustrators.
The only thing I'd add is the vital importance of stepping back to assess what you want in life and in turn, your work. I'm learning (albeit, slowly) that it's okay to catch your breath and get your bearings, that it's not always necessary to be scrambling pell-mell towards the Next Thing. Dreams are good, but burnout isn't.
Also, I still stand behind the advice to eat ice cream when the job calls for it. Or donuts. Your choice.