For me I just try and dedicate myself to knowing what I owe and stay committed. There are days given how big my queue is that I become worn-out completely and it takes a mental toll on me. It's easy to get bogged down, but in my particular circumstance I just have a drive to keep up good will with my clients and ensure that I don't slack off.

I guess if I had to be honest, I reflect on how artists have treated me when I waited on commissions and tried to work with them. I won't paint a broad brush because I have met artists who're great to work with and are kind/generous/etc. and you get a good feeling about them, but have also met others who generally do sloppy handiwork and are just in it to collect the money. So I guess you could say, "I don't want to be them." It reflects poorly on me if I fall into their habits and so I strive to do better and not follow them.

As someone who's job really is living off of commissions, my goal is to just maintain good relationships and positive feedbacks. I balance my time between finding time for myself, but sticking to a schedule in which I can dedicate at least a good 4-7 hours to one or two particular commissions. Scheduling. If the day goes by incredibly well I might even do more. The struggle can be a huge challenge and for everyone it's different, so my method might not be the best one for everyone, but in my particular case - I put on a 2-hour video of some form on Youtube as background noise (like an iceberg explained or retrospective documentary or even a longplay), fire up the program and get to work, haha. If progress gets done I get my rest and begin the next day. ^^

to be honest my biggest motivators are spite and hyperobsession with a character haha

I say this as a non artist and this is stupid simple advice but never forget that each person has their own ways.

I know you're just trying to get more ideas but hopefully if it ever doesn't work it doesn't frustrate you.