Ten Dialogue Musts

According to The Tools of Screenwriting: A Writer's Guide to the Craft and Elements of a Screenplay, dialogue in a screenplay must . .

1. characterize the speaker, and perhaps the person addressed.
   
2. be idiomatic, maintaining the individuality of the speaker, yet still blend into the style of the screenplay as a whole.
   
3. reflect the speaker’s mood, convey his or her emotion, or provide some window into his or her inner life.
   
4. often reveal the speaker’s motivation or an attempt to hide his or her motivation.
   
5. reflect the relationships of the speaker to the other characters.
   
6. be connective, that is grow out of a preceding speech or action and lead into another.
   
7. advance action.
   
8. sometimes carry information or exposition.
   
9. often foreshadow what is to come.
   
10. be clear and comprehensible to the audience.