Not Yet Overused in Urban Fantasy
1. Once there was an evil race which terrorized the universe/multiverse. They were defeated, but:
a. A few survived on a planet they call Earth (Michael Shaara, "All the Way Back.")
b. They were imprisoned in a space with only three spatial dimensions (Colin Kapp, Transfinite Man.)
2. Organizations which can accurately predict the future compete with each other to shape it.
3. All the technology we think is science-based is really magical.
4. Devils are actually the Good Guys. William Blake seems to have believed this, at least part of the time. (Note: If you want believable characters, don't write William Blake into your story.)
5. After a catastrophe, the only people left alive are a man called Adam and a woman called Eve. This one was overused in science fiction by 1950, if not before; I suspect it's not very salable in any related genre.
6. Men and women belong to different species.