Writing an outline for your screenplay is a good way to gather your thoughts before you start writing either a full screenplay or a treatment. An outline will allow you to flesh out your ideas and settle on ideas and characters that will eventually work its way into your screenplay. If you're unsure on how to write an outline for your script, don't worry, just follow these simple steps.
Research characters, action and other elements of the screenplay. Since this is just an outline the research doesn't have to be particularly thorough at this point, just enough to get you started in plotting out your screenplay.
Determine the arch of the movie before you begin to write out your outline. You need to know where the bulk of the action is going to take place, the denouement, if there are any surprises or false endings involved.
Break each scene down using the following information: whether the scene is an interior or exterior scene (INT. or EXT.), location of the scene and the time of day the scene takes place.
Provide basic information about your characters as you introduce them in each scene. You may not know a whole lot about them at this point but the information you do have will be helpful later as you continue to develop your script.
Write a brief synopsis, no more than a sentence or two, of the major action that takes place in the scene.