i think your art is realy good. i chasnged a fue thing i dont know if you like but i hope you do.i started by making the shadow more dramatic and drawo another eye on the left. i also make his hair and beard les spiki, and i also made the drwaing a litel les mesi

Nice character design here. For coloring you just need to choose a color. Then take that color and make two more colors from it, one darker in value and one lighter in value. This will give you the basic values you need to add depth. Then just use your freehand selection tool to draw interesting shapes for your shadow shapes and lighter shapes. Then you can add a brighter highlight color if you want. For hair, it takes the same approach. Choose a color and fill in your overall shape. Then pick out ribbons with the selection tool and fill with each value. You can do this with a brush as well but that can tend to get busy in you aren’t careful. I hope this gives you an idea on some things you can practice.