I'm rewriting a script that's been through quite a few drafts, and my characters no longer feel like characters. No, they feel like really old friends. Or maybe enemies, because they don't make life easy for me. Frenemies. They're shifting in front of my eyes, changing into something that might be better, or maybe worse. Either way, they're unrecognisable from the first-ever draft.
I'm not a writer who likes to know what her characters eat for breakfast, how they felt about maths in school and what their phobias are. Unless they have a phobia of clowns, and the script is about a pyscho clown. Or they hate their father, and the script is partly about someone being a bad dad. Some back history is important, sure, but in general I don't need to ask myself whether my hero ever suffers from dandruff or how he votes.
What I do like to do, and this has been one of the most helpful things I've ever tried, is to cast my characters in my head while I'm doing a treatment. Then, when it comes to writing the script, I write dialogue for that actor. If my hero's sidekick is a big, lazy joker guy, I imagine Seth Rogen playing the part and write for him. These days Seth would probably be playing the hero, but still, it helps to have someone in mind.
And it's not just stars. I often "cast" character actors in my head, people I've only seen in bit parts but who have the right look, or the right speech pattern. It helps to make the roles sound different, and hopefully one day it will make the Hollywood table reading pop!
Movie characters aren't like real people. They're braver, crazier, cooler and better looking than us. But having real actors in mind for your parts can make the difference between dialogue that sings... and a script where everyone sounds the same.