It looks pretty good for being uncertain about shading I think you did a pretty good job. I have a lot of trouble with lighting/shading myself. The important thing is to establish where your light source is coming from and adjust accordingly, for example if your light source is coming from the top right make dark shadows on the bottom left sides of faces, legs, stomachs. It's a simple concept but one I'm guilty of ignoring. It's so easy just to get caught up in what you're doing and not want to plan out where things go. The other rule of thumb is that things farther away appear darker. Anyway hope that helps a litte. Nice picture!

This looks really good. Is this supposed to be a Doberman? Looks like one :)