A. You need to add some flow compensating your render.
B. The top right looks empty.
C. A black and white render and your choice of background is not ideal.
D. You should add depth by sharpening closer objects while blurring farther objects.
I would like to see the finished project, hope these tips help.
Oh wow, the blue seriously kills it. What i'd suggest doing is saving the entire image like it was finished then put the saved image into the sig as a normal layer, blur it up alittle then set the layer options to Brighten. Give that a go.