Nice. I like the subtle details on the slothead thingy and you could kinda see the strings go through and stuff. You've definitely done a great job at shading his face though! I still have alot to learn on that. Nice hair too xD
cheap and easy way is a solid color or light gradient to compliment the colors of the figure. another way is a simple montage of a detail of either the face or guitar to highlight the work you put into those two pieces of the piece, usually its best to desaturate their background colors
I started with the everything that i wanted to toon as a coloured object; this is my base. The base had a rough shape of how the hair would look. I then added a layer over the base which i used for drawing in the darker hair (was was most of it). This dark layer also contained the hair that falls over his face. Then on the same dark layer i drew thin strands with the pen tool; pretty much just 2 anchor points with a slight curve between then. Then on another layer above the dark layer i used the same dark colour but set the layer to 50% opacity and drew the really thin strands that went both out of the top of his head and over his face. Then on one last layer i drew a few strands of lighter hair. Then later in the production i coloured in the base layer around his head with the colour i wanted it (using ctrl + U).