I think the face shape is awkward. It's too straight and unnatural, as if you drew it with a ruler. The hair seems way too unnatural and flat on the head, and the hair lacks the layered look. You only drew the outline of the hair. Try to use a blend of soft and hard curves.

I've skimmed through the above comments and it seems that you are still having trouble with proportion. Are you focusing on individual components? It's good to sketch a quick simple model to get the proportions (the biceps should be bigger and the arm shorter than the forearm, things like that) right and then work from there.

The perspectives (The positioning of the legs) and postures are unnatural also. The best way I found was to go to a starbucks or somewhere with alot of people and just examine how they move or stand. Actually this will pretty much will help with everything perspective, proportion, shading, etc.

I know it's alot of things to think about when you're drawing. Just draw and redraw until you get better and these things come naturally. Prefect does make perfect. And most importantly keep at it, never give up and you'll become professional manga artist quality. ^^