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.
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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.