/ic/ - Artwork/Critique

Newfag here. Need some help with some art work here. Haven't been drawing for very long and need a bit of help getting the posture right on this piece. I was hoping to make a women with her legs apart with one hand on her knee and the other on her hip. I also want her chest leaning out and forward. This is where I ran into the most trouble, it looks like she is slouching too much. I want her back to arch in a little more. Her shoulders are also a little (or a lot) awkward. I would greatly appreciate any advice and/or models you guys could give me. Thx