For sure @frankenstejin ,
first i put all the colors on the character, after that i create a multiply layer, than i select black color and paint in hard. I have chosen a top light source on this case, and paint the shadow in hard. Than i look for the areas that has cast shadows and maintain, area that has no cast shadow but the soft shadow i blur it, because the light fill that part instead of a projection of something, so change the opacity of the shadow, maybe 45%. After all i paint the smaller shadows of the intersections of the character, something like ambient occlusion. For the final, i put some light reflections.
I guess that is it. hahaha. You have a lot of ways to do the same thing, this way works for me.
Below has an example, maybe could help my explanation.
