*grabs red pen* MWAHAHAHAHA!
Your lines and shading are pretty good but it seems your biggest problem is anatomy.
Are you using the "sketch skeletons" method were you sketch out a wire frame and then bulky shapes on the frame and then finer details?
It helps to have a ref pic when drawing people so you can tell if your perspectives and proportions are right.
Deviant Art has a lot of stock images to use as references.
Here is a link! If you have a problem with nudity, be sure you have the filters on or are logged out as some people like to use nude stock refs and perverts post nude for their own reasons and label it "stock" so it doesn't get flagged.
The best anatomy ref pics to use are simple nude or close to nude (body suits/leotards/ect) poses.
Once you have the anatomy sketched down, then you can draw out clothes on top, using the body you sketched as a reference for where clothes should bulge/bunch/fold/ect. . .