Uf, in this drawing in particular it was easy since it's a fanart I took the color scheme of the original characters and played a bit with them. When it's an original drawing... well, it's difficult. I try to choose two or three colors that combine well and paint the most part of the drawing with them. Take a look to this tutorial, it helped me a lot! [link]
M'encantaaaa!!! és super divertit! les versions de sota individuals que van de negres també molen molt, sembla tret d'anuncis de roba o algo jajaajja <3
Good job!