How to create an atmospheric rainy scene?

Hi there community.

I’ve been trying to work on a scene thats been going on for a bit too long and thought to take to the community in hopes to find someone that would know or know of a tutorial or something I could learn this off.

I’ve been trying to create a scene like London or, in a gaming perspective, something like bloodbourne. Dark, rainy thick fog, cloudy (I can’t seem to find anything on clouds so even if you only know about that please tell me) and things like that.

Thanks!