Dialogue Do's and Don'ts

When the screenplay has been written and the dialogue then added...then we are ready to shoot! 
A. Hitchcock.

Dialogue is one of the major blind alleys that new script writers run headlong into.
Before you add dialogue you should be sure you already have a few things in place:
Beginning/middle/end of the story.
Clearly defined needs/wants/problems of main characters.
Synopsis which can help you, the writer, maintain focus.

Characters need to be placed into a plot structure, you need to know what they will be reacting to or setting up before you can decide what they will be saying to each other.
Writers need to know the goals, problems and character objectives first.

Film is about action and visuals, dialogue is for the stage.
Know your story events and build your plot outline first, add dialogue last.

Less is more!

Read successful scripts, you'll notice that there is very rarely huge blocks of dialogue.
Usually there will be a line, followed by a line, all the way down the page.
The first thing to ask yourself about the dialogue you have written is
'Can I cut a word without losing any impact?'
'Can I cut a line without losing anything?'
'Can I cut the whole piece and give the same information using visuals?'
FILM IS A VISUAL MEDIUM.
Have a look at Tom and Jerry; no dialogue yet still very entertaining:






 Directness is usually best. If a character, Lisa, hasn't seen her boyfriend, Matt, for a while and she sees him in the street, here's what she shouldn't say:

LISA

Er, Hi Matt. Ah look, I was 

just wondering why you know, you haven't called me 

for a while and well,

I really miss you, and...

To the reader, the character seems weak and uninteresting because of the dialogue. Think about her motivation for the scene.

LISA

So, Matthew, where do I stand?

This is better, simple and direct, she is now in control and a much more believable character. The onus is now on Matt to provide a good answer.

Maybe this is even better?

Matt advances toward her with a big grin on his face, as he reaches her with his arms open wide, she...

Neatly sidesteps him and strides past, without a backward glance.

There are many variations once you have decided what type of character Lisa is, she could slap him, grab him and kiss him passionately, grab and kiss a passer-by passionately?

Positive action and decision making will endear your characters to the audience.

In the feature film, Citizen Kane, the characters Kane and Emily's marriage breakdown is conveyed by cutting most of the dialogue and simply showing their breakfast becoming more and more estranged each time, sitting further away from each other, body language, reading different newspapers.

Give your characters individual voices rather than your own.