One of the most basic way of coming up with story ideas is to take a familiar story or thing, list out what’s commonly associated with it, then start changing some of those elements.
For example, you list out all the normal things for vampires–the coffins, black, bats, sucking blood, etc.–then you begin to twist. What if the vampire wears, instead of black, some styling plaid? What if it isn’t a person but a rabbit (whoops, that one’s been done)? What if instead of gothic places like catherals you find him in a trailer park? What if instead of being dangerously suave, he’s a drunk?
Do you see? You can do this with anything.
In this interview, Matthew Sturges talks about how he did just that with the movie The Dirty Dozen and ended up with with Midwinter, a novel about prisoners given another chance. According to Sturges, “In the case of Midwinter, the beginning of the story was, ‘What is prison like in Faery?’”
Read the whole interview. I think you’ll find it enlightening.