I’ve been working with a writer who has been struggling with her heroine’s dialogue.
The problem is that the heroine speaks in cryptic sentences that the other characters can’t respond to. To correct this, I had her write an interior monologue about the heroine doing some simple task like getting dressed for work, a technique used effectively in the recent film, The Informant.
Even if you don’t actually use this monologue in your screenplay, it still works as a great exercise to get a sense of what your character’s thought process is like. Not only will it help your character’s dialogue (you’ll learn how they talk) but it will provide important insight into what they notice about an otherwise unimportant activity.
Good luck and happy writing.