List your five favorite books, movies, or TV shows.
Cats Eye, Breaking Bad, Shawshank Redemption, Cloud Atlas, Friday Night Lights.
List the tropes/components in each that you like.
Cats Eye: toxic female friendships, relational aggression, girls who don't fit in with their gender stereotype.
Breaking Bad: fish out of water, close male relationships, father-son dyad
Shawshank: close male friendships, stoic males, escape plots/ "I Love It When A Plan Comes Together"
Cloud Atlas: revolution, escape plot, reincarnation, notion of doing small good in a world of bad
Friday Night Lights: small town, healthy marriage, earnest learning of lessons
Take several of the things that appear more than once and just put them in the same story. My first novel has some fish out of water stuff with both main characters, an older brother-younger brother dyad, a stoic male (and female), a hell of an escape plan, and the notion of a world of bad and what we do with that. (Is Boston a small town? Kinda.)
A different book, the one I'm revising right now, was generated this way. I loved when Veronica Mars went to college and just wish the show could have spent years and years there--it's such a perfect environment for mysteries. I'm also a psychologist and have noticed that many people have more than just a passing interest in the field because any person can relate it to themselves. I also like stories that take place in a closed environment. And will-they-wont-they flirty friendships. Thus, I'm writing a thriller that takes place in a college, involves a large-scale psychology experiment (somewhat based on reality), and a toxic dyad at its heart.
When all else fails, click here and pick three random tropes.