ok, first of all. you got a pretty ok start here. but you got to think what shapes a head has. even though it is manga, it is anatomically correct, when it comes to the shape of the head.
a head is made out of a ball, and a cone. At this point, yours look more like a bean.
Here , i drew you an image to explain a bit more:
Though this makes the head look really big, but when the hair is on, you will see it is correct.
Here is another one of my drawings with hair:
If you get the shape of the head to look more like this, i think the whole model would look better, but hey.. that's just me.
(ps: sorry for my lousy manga drawing, it was just to show an example xD)