I'm not entirely sure if you use it or not, but if you don't use layers to color in your work, then I'd suggest trying it out to help your coloring go a whole lot smoother. The way you color in things seems like you just color over the lines you already drew, and then just tried your best to fix any mistakes (which I give you a lot of credit for, your art looks so much cleaner in comparison to others who don't use layers or don't know how). I'd also try to learn more on how to use the opacity meter to shade in certain parts of your work. Shading things can be a pain here-and-there, but it's worth it to know how to do it. Other than those two issues, I don't really see any other things you can improve on.

I've never really seen you or your O.Cs before, but looking at them now, they're definitely designed and unique.

I love your O.Cs! They look so cool! Keep drawing and improving and you'll do great! :D