I've been thinking of this a lot for some time now.
Artists, who made a "tutorial/guideline" to prepare yourself for this, advise a couple of things:
"Don't sell yourself under value (that means minimum wage of your country!)."
Yeah, this is probably the main aspect speaking against me taking commissions ever. The amount of time I need to finish a picture in relation to the quality of the result - also depending on whether it's a sketch, lines, full color etc. - would cause me to charge waaay too much. Also, to trustworthily verify the time I have actually been working on something would require me to stream my drawing process and safe a video of it in order to have proof. Too much effort for too little (non-profit) gain.
"You should start taking commissions after you've built yourself a fundamental fanbase."
I am definitely not an artist a lot of people know, so this is out of the question. The only thing helping me to improve (sry) this would be by drawing more and getting better. Taking requests helps with this, too.
"Be mentally prepared for black-sheep-commissioners."
This is also a very touchy part for me, since I have been attacked via PM before for no apparent reason (mindless hate?). I also imagine it to be tricky cancelling a commission for me; maybe I'm just too nice. =/
"Be aware of the fact that your followers/watchers might lose interest in your work after you start taking commissions."
I don't have that many followers/watchers (thanks to everybody who does follow/watch me! ♥), but losing them would feel bad nonetheless. It also affects point 3. and some people might get scared of (non-existent) paywalls.
These are just some of the points that other artists mention about taking commissions, but I felt like these stood out a lot.
In my opinion, I will not start taking commissions for at least another year or so, because I feel like I have to improve a lot more to maintain a certain standard in quality. However, I have seen artists that started taking commissions (successfully) a couple of months after they started drawing. So is this based entirely on your own self-confidence? I also believe that it depends on what you are willing to draw for others, but I would not cross my limits to do something I dislike.
And now, I don't know what I should focus on here. =/