Alright lets see..
Color -- The colors are way off. Usually you want to pull colors from your focal point, in this case your render. With her, you would want to use reds, yellows, oranges, & blacks. This is important because when you have too many colors that don't match at all, your eyes start looking everywhere instead of just the focal.
Depth -- The background should be slightly blurred and your render should be slightly sharpened. This helps bring your view directly to the focal.
Placement -- Normally try to avoid placing your focal directly in the center of the canvas. Using "The Rule of Thirds" is much more appealing to the eye naturally. Here is a link to see what that is --
http://en.wikipedia.org/wiki/Rule_of_thirds
Also, your effects don't really flow well with the render. Normally, try to look at your render or stock photo and see what theyre doing or what is going on. In this case, shes got a sword with some flame type effects coming off of it, right? You would then choose effects that kind of match that such as flames, sparks, light strokes, etc.