Since it's the beginning of the year and I'm busy trying to clear out the last remaining part of last years commission queue, it's probably a good idea to consider what does and what doesn't work while I'm reorganizing.
What does work definitely seems to be sketch commissions and sketch commission streams; these made me the most money in the shortest period. And they leave me lots of time time to pursue my own projects, which seems to help prevent me from burning out, at least somewhat.
Longer commissions and other similarly large projects don't work as well, though a large part of that is that I'm just god damn slow as hell.
Ultimately, because of my slothiness these projects just become a source of a huge mental load for me as I start to fall further and further behind on them. I don't exactly want to stop doing these kinds of projects, but I suspect I'll have to sharply limit the number I take on at any given time.