Try to use a variety of different colours in your art -- Experiment and be creative!
For evample: your first picture, the "soriku-2" one, you've coloured in sections all one colour. How about giving her hair some different tones? like a darker black and a medium grey? That would look nice, maybe with some white highlights too?
:)
But your drawings are good, i like them! x3
EDIT : Here, I just did a quick edit of one of your drawings (hope you don't mind ^^; )
http://i26.photobucket.com/albums/c1...rest/edit1.jpg
See where I've gone around your lines with some darker colours and highlighted some parts?
That's what I was on about above.
Of course, it doesn't look the best because Im not an expert, but it'll get you in the right direction ;)