Welcome! First off, I love, love seeing original fantasy costume concepts. It's one of my things, so that gives me a bit of natural interest in what you have here, even if I'm not keen on the practicality of it. Unless she's a dancer/performer of sorts, then it's a little more fitting! The proportions are not bad, but the pose is stiff and awkward. It does not feel natural. I'd start with using photo references for poses until you get a good comfortable feel for them. The lighting is definitely off and not defining her shape much, making her look very flat, especially in the face. I know for a lot of people starting out with fantasy, especially when pushing a particular idealism, are deathly afraid to touch the face with shadows and highlights. Don't. Get out of that comfort zone and add shades and highlights in her face as you would any other part of the body. If you mess up, and you will, we all do, it's a learning experience, not a failure. You'll do better the next try. If you never venture there, your character's faces will just never look natural. Face Lighting Example
I don't know quite what to say with the shadows in how you could fix them. It would definitely require a redo. One thing is if the light was coming from the front like that, she would cast a shadow on her cape, in which you have no cast shadow present, just a weird side shadow that doesn't make too much sense. Don't forget that light bounces (like so), which would help you more in defining the form. Also you need more definition from the skin and the cloth. It looks like most of her outfit is painted on her, rather than fitted.
I hope to see more from you. Also try adding a hint of an environment, even if it's just a ground shadow, so you don't get too many floating characters.
