Best way to improve is to show others and get feedback. I myself am not an artist so I can't say how to improve or anything...but This one that I 'quoted' was by far my favorite (even though I really like Saguru and didn't know who the second people were in either of the crossovers). The girl in this one kinda reminds me of Avatar: The Last Airbender for some reason. I hope you get advise and help cause you are much better then me (I especially can't do people) and that starting point can help you go far. Keep at it.
wink