Agree with Connie, your work is quite wonderful and even your lighting skills are good enough IMO, just you need to render stuff out in layers and try combining them in more interesting ways. eg this

http://excalibur.renderosity.com/mod/gallery/index.php?image_id=1331971

pic of yours is well lit, but it can be made even nicer:

1. Decrease the sat of the background and increase sat of the girl in the forground
2. Add blur to background elements and color correct them to be bluer.
3. Add slight amount of specular bloom to the highlights for a more fantasy/old world look.
4. Adjust the brightness and contrast slightly and lessen the green cast of the scene.
5. Add slight grain to the image.

Ideally I would  render the girl, the balloon and the backdrop separately and composite them together in PS.