first you should make your sigs smaller like 300x125 or something there way to big
second try to go with the flow of the render (flow is basically having everything be going the same way)
third use C4Ds that go with your render
fourth make sure your C4Ds and effects have a almost the same color scheme as your render
fifth use text that goes with your render
sixth use a a background that goes with your render or a stock image
I suggest use tutorials.. if you want i can send you some of you can go to planet renders
and don't take this in a bad wy build your confidence and you will do better