I don't believe you've asked me to look over your work, but if you have, I apologize for not getting back to you prior. As for your work, I'd say you have a pretty solid foundation to build upon. I would have to recommend a few things, primarily with your human and human-like characters; while I can tell you are going for more of a manga/anime style, anatomy is still an important aspect. I'll use your Matoi Ryuko Doodle piece as an example. THe line work and costume are well defined, but the peanut shell shape of her left arm makes it appear as if she doesn't have an elbow. Also, and this is a fairly common thing among artists, myself included, having shoulders wider than her hips is a more masculine attribute. Plus, the distance between her belly button and crotch is way too short. Hopefully you don't feel as I'm picking on the one piece, it was just a good example for me to throw some tips your way.
To best improve, look up some of your favorite manga/anime artists and look how they approach their figures, both in sense of line work and anatomy; there's a ton of awesome tutorials/references here on deviant art. Second thing I would say to help improve your work, step outside your comfort zone. Look at some comic book artists that take a more realistic approach (or at least very different than yours), and try to mimic their styles. Study their lines and poses. Once you've drawn in a different style for a bit, return to yours, and you'll find yourself picking up little things that you had never thought of before. This is a good approach every time you feel you've plateau'd/peaked skill-wise as it helps you find new techniques and approaches to drawing.
Hopefully this helps, and if you have any other questions, feel free to ask.