Nice pose, interesting lighting, basicly this looks great to me, but you asked how to improve it, so what follows is mostly critical. I think the image should be lighter and have much more contrast. I'm not keen on the skin tones, I think they should be more towards the blue and a little more red. The highlights in the eyes (on left image) are a nice touch, but perhaps a little over done. The left elbow could use some post work. The lock of hair on the forehead could be softened at the edges. I find that a good skin texture makes a big diffrence, investigate what is available for your figure. In the end, remember that this is just my opinion, and highly subjective. Ten people would probably give you ten diffrent answers. One more point. Part of the knickers is hidden in the hip, you could use a magnet to pull it out so that it is visible again. I am posting a comparison image to show how I would postwork it (click on the image to enlarge it), hope you don't mind me taking liberties with your image. The postwork was done in PaintShop Pro 5.