Okay, I'll say right now that I'm very much learning how to get good at siggie making myself, but as I realise how frustating it is to want to improve but not have anyone telling you anything to help you improve, I'll give it my best shot

.
However, you may not be that interested in reading what I have to say as I have never once used a c4d as I don't even know where to get them from, but I manage fine (well, for my standard

) without them

. I'd check out just the tutorials at codex though as they are pretty good, if that doesn't work there may be some on deviantArt?
Anyway I know when I didn't have c4ds and was trying to use something similar, I found pictures of water drops and smoke and that sort of thing worked okay, though I just try and use stock appropriate to my siggie these days. So maybe you could try that if you're looking for a way to fill in space?
I've also found that selecting your focal and copying it to another layer lets you kinda cheat with what you can do to it. I'm best at images where you just have a render and make up your own background you see, so when I tried to do pictures with background already in I hated that you couldn't really do anything and have it nice and simply behind your focal, until I just did that

.
There are a load of good tutorials on codex to make sigs that don't rely on c4ds at all, I'd recommend taking a look at those, it'll help you develop your own style

.