I like the scene in the first 'Scream' movie where Sidney gets up, and dusk is falling, and she's looking out at the hills of Santa Rosa, there where it was filmed, and that's where you sort of hear her theme being played out. I always liked that moment because, to me, it became more than just a horror movie.
I usually start from the most general to the more specific. I'll get an emotional overview for the film as a whole, trying to pinpoint what the musical identity is and come up with thematic ideas - any ideas that identify as succinctly as possible what the film is.