Too many people think there’s a process list or magic trick for this sort of thing, and there’s not. Write and revise and write. Isolate the things you want to write about and the things you want to say and, really, just bloody well write them down. Screenwriting courses and creative writing guides have given people the idea that there’s a miraculous cheat sheet for doing any kind of commercial writing, and it’s bullshit. The idea works or it doesn’t. You’re either good or you’re not. And if you’re not, keep writing until you are. That’s it.