tsujoi's got the gist of your problems down.
First off, her legs are way too long. They are almost twice the length of her torso. Either lengthen the torso or shorten the legs. Secondly, her waist is too narrow. I'm not sure which view you're drawing from, but to me it looks like her body should be twisted a bit. This means that we should be able to see more of her side. It looks like you're thinking of her body as a flat object; instead, try imagining pieces of the body as 3D blocks- when you view a block head on, you will only see one side. Turning it will allow you two see two sides, and you should apply that principle to your drawings. Thirdly, her breasts seem a bit too high, and her hips are nearly nonexistent. Look at some reference pictures!
I've done a little redlining for you to help you out. The pose you chose is a little complicated, and I'd definitely recommend studying up a bit more on human anatomy and practicing building form with shapes before tackling another pose like this again.
I drew a little on the side to show you what I meant by flatness and form.
This is just the redline by itself to let you compare it to your drawing (her legs might still be a bit too long).
Just practice drawing some human bodies and you'll get it! Hope that helps! :)