Also, stand in front of a mirror and make the pose yourself. Her right arm looks like there is no bone in it and it's just flopped on top of the rail. Look at your arm from your elbow to your wrist is basically a straight line, or a bit curved outward. Also, to keep limbs looking the same size make a ball and rod sketch before you start the outline so you can tell if they are the same length and look like they are in a natural position.
Also, with your shading think of a light and shade what is on the opposite side of the light. Also I don't know what program you are using, but with photoshop or paint shop pro use the line or pen tool to make straight lines like with your railing.
I also notice you have a bit of problems with clothing. In that case i think the best advice is to just go with the flow and think of gravity. As they said above looking to stock images and real life and analyzing them should really help you.
The rocks in the background look kind of like plastic. Here is a tutorial that should help you there. http://shadowumbre.deviantart.com/art/Various-textures-tutorial-46100062
The complexity of the costume is done well. I like how you actually have straps, chains, and buckles holding things together. Sometimes when costumes get too complicated it looks like the pieces are defying gravity.
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