Okay... Here's one I did a few months ago. Let me go ahead and make a self-critique.
btw... I have had no formal training nor do I know correct terminology when dealing with digital art nor traditional media. So please be a little forgiving if I unintentionally say something stupid.
1st thing I had issue with on this piece is the lines. I've been a tattoo artist for 10 years and smooth lines were a MUST but I'm having a really hard time getting my lines to be smooth and not "shakey." I was using the scratchboard pen tool here. I've since switched to pencil which I have better control over but sometimes I don't want that sketchy look than the pencils give. I wanted good solid smooth lines to give this piece the look of a precision carving but couldn't pull it off.
2nd problem I had was that I did this piece on multiple layers. I used the airbrush tool for coloring and then used the blender tool to try and gradiate the colors. I kept picking up white from the edges and ended up with a mess of muddy color. I haven't found a tutorial that I can understand exactly what tools are being used in the coloring prcess. I've read about using masks to quickly color "cartoonish" pieces like this one but I don't understand how to actually create and use them. If someone would be so kind as to point me in the direction of some easy to understand guide, I would be greatly appreciative.