How to Write a Script
1. Get your story straight. Come up with a specific idea of what you want to happen in the play or movie. Create the premise and purpose of that story. What are the circumstances and what are the goals of the story and main characters involved?

2. Your characters will drive the action on the stage or screen, so make sure you make them interesting and innovative. It may not be necessary for you to develop all of the characters right away, but some writers need to have everything set out before they can begin working. Find your method and work with it.

3. Create an outline or treatment. Before you begin actually writing dialogue and script, it might help to create a basic roadmap of what will happen in your story. Sketch out a general plan and envision how events will unfold. This should be told in the third-person.

4. Maintain your style. Remember, scripts are all about action and dialogue. Make sure your characters speak realistically, and try not to mix styles of speech and vocabulary too much unless you are going for a certain effect.

5. Ensure that different characters have their own 'voice' based on their background, which will affect their word choices and dialect. This will stop your characters from blending into one another.

6. Set the scene. Don't forget to include important details such as time of day, setting, and actions of the characters in the scene. These are nearly as important as the dialogue that occurs.
7. Format your writing. Skip lines between one character speaking and a different one speaking, especially if you're handwriting it. This will enable those reading the script to distinguish between speakers more easily, and also allow space for notes.

8. Edit yourself. Continually revise your writing, and, if possible, show the script to a friend or adviser who has writing experience and can critique and improve the script as needed.