When I'm writing a script, I don't worry about plot as much as I do about people. I get to know the main characters - what they need, what they want, what they should do. That's what gets the story going. You can't just have action, you've got to find out what the characters want. And then they must grow, they must go somewhere.
Every human being has hundreds of separate people living under his skin. The talent of a writer is his ability to give them their separate names, identities, personalities and have them relate to other characters living with him.
The brilliance of Max Brooks is that he always quotes authorities at the back of his books that never existed. Like a Russian professor he made up that validates a story or character.