Not wanting to get too off topic here, but I believe some of those images could go with some retouching for the brightness and contrast. Some of them seem too bright, or you can't make out the lines. A simple image editing software like GIMP could fix them right up.
I always had trouble with that, both in school and for my current works. I always rush my work when I'm near completion and that makes a sloppy result. I think getting an well presented image is as important as the image itself.
As for the actual drawings, I think everyone who attempts to draw characters would do well with some anatomy lessons, on the internet or otherwise. It may seem boring, but the human anatomy applies in more cases than just humans. Most animals use similar bone and muscle structure albeit with different proportions, and I noticed when browsing trough some monster concept arts, they also seem to base heavily on the human form, although extremely exaggerated. I found this website recently with lots of references
, there may be some mature references there, it's anatomy after all, but it seems to have very good information for all skill levels.