if you are an artist just trying out commissions for the first time as holidays come up, my advice to you to avoid burnout is have a clear ToS that states what you do and do not want to do.
not what you can and cannot do, but what you do and do not want to do. don’t try to be the cheesecake factory of commission artists and take every single commission even if it doesn’t suit your style or preferred subject matter. don’t write a little disclaimer about how you aren’t very good at backgrounds or vehicles but will do your best; that’s how you get a client that for some reason wants a full brooklyn cityscape from you and suddenly you have spent five months stressed out and guiltily avoidant of other projects. just say you aren’t offering backgrounds.
if you’re not interested or confident in concept and design, be clear in your ToS that you need specific references for things like clothes and features. coming up with design ideas is a completely separate skill from rendering them; figure out with what you are comfortable before accepting the task. a lot of clients themselves don’t understand that saying “do whatever” is basically tasking you to design for them, something for which you are well within your rights to charge accordingly.
pick your niche and hone it, and stretch your comfort zone with private work. you’ll figure out as you go just how far your comfort zone stretches and can update what you offer accordingly.
Having both been refunded and had to chase artists down for a refund, I’ll trust someone who’s refunded me for more stuff in the future because they were honest enough to say “hey I’m in over my head, here’s the money back.”