You are clearly progressing throughout the thread.
Alot of the pictures seem to lack depth, but ican see you getting more of it in your later ones.

I think the best advice I can think of may make me sound like a d*ck but...
Sticking to a strickly 'Anime/mange style of drawing' will severely stifle your progress as an artist. I've known enough people for enough years to confidently say that as a fact.
Try some other styles then go back to the anime look, you will see a significant difference.

For an immidiate reference check out Gypsy Elder's thread.

A good artist to check out for depth in contour drawings would be Robert Crumb, personally I find his art ugly, but i can't think of anyone who captures depth with line counours anywhere close to how well he does.