Don't use photoshop. Use Paint.NET. One thing you should do is instead of using the pencil/marker tool, use the line tool and use it to make curves. Your drawings all look really messy and the shading is inconsistent. Here's something I did a while back:

Take a look at the shading. It's consistent all the way through. I chose a light source and directed by shading endeavor from there. You just throw a little shading in a few places. Read this, all of it, or just look at the pictures to get the gist of what I'm saying:
http://www.artinstructionblog.com/drawi ... -and-shade