Anatomy and line weight practice I guess. I stole a clothes magazine my sister has and drew one of the models in a manga-ish form. Gotta say it really helped; whenever I draw girls, they end up looking like guys. So to all you artists who want to learn anatomy, work off of real subjects!!
Also, if anyone wants to take a crack at coloring this one, feel free to do so (just be sure to give me credit for the lineart). PM me if you want the bigger version. I'll probably submit a colored version later on myself.