When making a signature, you need to imagine it first. For instance, imagine how you want it to look like, then get resources that matches what you have in your head, you can Google specific things, like 'Dark C4D', 'Shadow Castle', 'Demon effect', etc. Next thing to do is to make sure that your render is the focus on your artwork. You do that by not making your signature filled with different effects. The maximum of effects you should be using is 3. For instance, 2 C4Ds, and 1 Fractal, or 1 C4D; 1 Fractal, and 1 type of brush - It's your choice. Adding many things at the same time will make it a big mess.
Try to use stock backgrounds instead of trying to make your own backgrounds. Use something that works with your render. Also, try to learn how to use 'Exposure', 'Gradient Map', 'Levels', and 'Curves' Adjustment Settings. Also check the Fliter = Blur, and Fliter = Smart Sharpen effects. All of this should help you getting better results.
