1. Zombies.
2. Parallel universe.
3. Time Travel.
4. Faux Steampunk (add a pair of goggles and an airship)
5. Getting revenge. AKA Kill the bitch. Particularly popular with high school students getting even with the bully.
6. Fairytale retellng.
7. Mermaids.
8. Edgy stories - rape, racism, incest or anything else intended to shock.
9. Pregnancy horror
10. Pun or twist at the ending.