First, your script must be in proper movie script format. All published movie scripts are published exactly as they are formatted for submission to a production company. To ensure your formatting is correct, use script-formatting software that formats automatically as you write.
Format your script as a shooting script. This differs from a spec script. Most scripts that are published are shooting scripts. These scripts are the ones used in the production of the film and contain camera directions and scene numbers. Automatic scene numbers can be turned on or off within your script-formatting software.
Save your script as a PDF, Word document or Rich Text document for submission by e-mail. You may need to print out a copy of the script if the publishing company you submit to only accepts postal submissions.
Write a short introduction to the script. This is the only addition necessary to a published script. The introduction gives a synopsis of the script, introduces the screenwriter, discusses the writing process and introduces any special notes concerning the presentation of the script being published. A published script is the focal point of the publication and needs very little introduction. It is acceptable to add bits of trivia throughout the book regarding the shooting of particular scenes.
Locate a publishing company that specializes in publishing movie scripts. The best way to do this is by using the "Writer's Market" and scanning the publisher listings. Make a list of all companies that publish movies scripts in the same genre as your script, then write a query letter pitching your script. In your query letter, introduce yourself briefly, give a synopsis of the script and ask the publisher to consider it for publication.