To start with the positive aspects of this works, it has a nice, ethereal floating feeling to it with the flowing garments and hair standing up as if she were falling or underwater. I like the shadowing on the subject for the most part, and you seem to have a good grasp of proportion, although her left foot seems a little long to me. The backdrop of birds against a starry sky is good, but the blank white spaces at the corners of the work are rather distracting-I think it would work better if the entire backdrop was a starry sky, or if it were at least a dark color, so that the foreground pops more. The composition seems well laid out to me, save again for those blank spaces, and the figure looks quite dynamic. As for areas for improvement, perhaps you could establish the light source on the figure a little better, so that it's clear which direction the light is coming from. The back leg could also use a little more definition, as it looks like an outline more than a limb. These are minor complaints, though, and overall it is a fine piece. I hope this helps you improve it.