Okay so in order to make this particular peice a little more natural put more shading. maybe add a couple of straight black lines for charcter. (love the art peice btw) shading can play a big role in art peices too much aand it gets sloppy to little and it gives a cartoon vibe so go threw trial and error to see what fits your style. I would attach a art piece that could help but i don't have enough time to create one. if you need it though i can make a cheat sheet up with anything you want.
