A few things, in any order. Zombies, vampires, werewolves, fairies, demons, (or faeries, daemons if you prefer) mean teen-age girls, clumsy teen-age boys with secret powers. And mindmelding dragons.
Time travel is a perennial favorite, as are doomsday prophecies from lost civilizations. Wizards, demi-gods, and boarding school/finishing school.
Any combination of these will do.Fairy boarding school? Time-traveling vampires? Dragons in the Temple of Doom, Zombies in corsets? Wait- that's been done. (Pride and Prejudice and Zombies. I read the first two pages while browsing and it looked amusing.)
Nobody wants to hear about vampires any more, right? Whatever. Half the paranormal books out there are about vampires.
You can just pick a few of these elements, mash 'em up and presto! You've got a best-seller, right?
Five ideas in five minutes-
-jealous teen-lost-spirits try to affect the outcome of a beauty contest.
-a wizard and a witch are transported back to cave man time and establish civilization.
-Astronaut is bitten by a werewolf and sent into orbit before he realizes what happened. His space ship orbits the full moon every eighty minutes.
-A zombie falls in love with a succubus and tries to win her affection via multiple blood transfusions. Then his head falls off and mayhem ensues. Gross.
-A fairy gets fed up with being pushed around by other mythical creatures and summons a demon army to bend the forest to her will.
What do you have? C'mon lurkers. Throw me a bone:)