Uhm watch the last piece, the anatomy seems kinda broken the hand that's higher seems to bug for her body, her torso seems kinda short, and her head is really pushed back. You have some skill for sure, just keep working and polishing that skill!
from what I picked up in the thread is the most common expressions I see are the typical happy, sad, neutral, and I believe one mad. Mostly happy and neutral. I see a lot of round cheeks and pushed up lip lines. xD I would adore to see some rage in there. Draw some gaunt and square faces too. Get out of those round cheeks. Draw fear. Insanity. Pretending to be happy. Pain. Defeat. Go beyond the generics.
I have a great book recommendation if need be. I found it at Barnes and Noble and it should be able to get ahold of. It is called Facial Expressions by Mark Simon. It has a butt load of visual reference from all ranges of expressions as well as various models of different face structure and ethnicity.
If you can't afford a book, look in to Charlie Chaplin and Buster Keaton. Both of those men worked heavily in the Silent Era of film and are geniuses in regards to facial expressions and body languages. Really, just explore the silent era period. It'll help gain a feel for expressions. This was a time when stories could not be told through words after all. :]
I always like to see work in progress stuff and I think you're doing great with the photo studies.
You should try and get away from using only outlines in your figure drawings. It looks like it's keeping you from getting the proportions down correctly. Do some quick drawings focusing on light and dark shapes for example.