Alex, I have a few suggestions to improve drawings.
The current shading is really dark. Usually when I'm shading with one color, I only use colors at least 16 notches brighter/darker than the base color. Another thing is that you should really use smaller outlines, this way you can not only add more detail, but have smaller characters so you can add more content to each image.
And lastly, try to have a little more consistency in the outlines. Other than that, you're doing fine.