Some tips on writing dialogue

Dialogue has two functions, to give information and to reveal character. It represents the internal and external life of your character. External dialogue is what you say; internal dialogue is what you mean.

• The way a character speaks provides the context of the character’s world in terms of culture, class, age, region, time, education, attitude and personality.
• Listen to your characters speak. In an orchestra different instruments make different sounds. Your characters are like instruments. Each voice has to be distinguished.
• The basis of good dialogue is conflict. Set up your characters in conflict, not conversation.
• Keep dialogue lines short, one or two sentences, avoid long speeches (a monologue is another story.
• Good dialogue illuminates what the character is not saying, the subtext. It reveals your character's inner life, its wantings, its true intentions. We almost never say what we think, and people who do are usually are defined as mentaly ill.
• Dialogue will move your story forward: it's the external dialogue. Decisions, commands, spoken intentions.
• Motivation is action; the audience should see motivation, not hear about it.

And remember, with different film styles go different dialogue style. Charlie Kaufman said in an interview that the work on the dialogue for Internal Sunshine of the Spotless Mind was very easy, because there was a very natural style to it. The characters just spoke. Being John Malkovich, on the other hand, was a much more stylezed piece, and demanded a very thought-of dialogue.