Select a theme you want to explore for your main character. For script writing to be effective, it must be steeped in some thematic underpinning. If this isn't the case, the story may feel generic or derivative. Broad themes include man vs. nature, man vs. man and man vs. society. By selecting a theme, it will give your main character direction.
Flesh out who the main character is at the start of your story. In good story telling, the main character is put to the test when conflict arises. Very often, the conflict should test the weaknesses that the main character has in life. However, the converse side of fleshing out your main character's weaknesses is to find the positive traits he or she possesses. Over the course of the story, he or she will rely on these traits to overcome obstacles.
Create a world for your main character. This world needs to supply the environment that allows the main character to go on his or her journey. Characters often start from a low point and ascend to a high point. Conversely, characters may start from a high point and get knocked down, only to try find a way back. As you create your world, think about this trajectory and how it fits in with your setting.
Create the beginning, middle and end of the story. While there are countless ways to craft a story, some of the elements are universal. In the beginning, you are introduced to the main character and his or her world. By the end of Act I, a major problem presents itself. The middle of the story tests your character's weaknesses as he or she tries to rectify the problem from Act I. However, complications in Act II arise when a character is suddenly faced with a new problem that threatens everything he or she has learned. Finally, the end of the story asks that the character use everything he or she has learned along the journey to either pass or fail the final mission. The character at the end of the story should either be wiser for what he or she has learned or suffer the consequences from not learning the lesson.
Learn about the screenplay format. Writing a screenplay is about the economy of the word. Unlike a novel, a movie script is about 100 to 120 pages in length, while a television script for an hour long drama is comprised of 50 to 60 pages. Programs such as Final Draft, Movie Magic or Scriptware are popular programs that format scripts automatically. You will not have to worry about learning the proper spacing as simply hitting the "Tab" or "Return" button will take you to the appropriate next line.
Type the "slug line" or "header." This component has three major parts. It notes whether the scene is an interior or exterior, the physical location and the time of day. Interior and exterior are always denoted as "INT" and "EXT." The location is the actual name of the place. The time of day can be the actual time or the time in reference to the previous scene. For example, the first shot of "Back to the Future" might be written as: "INT. DOC BROWN'S GARAGE - EARLY MORNING." Notice the dash separating the location and the time period. Also take note that this line is always in capital letters.
Add the action to the scene. Generally scripts have a small amount of action at the top of the scene. The action is then described as needed throughout the rest of the scene. The trick is to write the action as economically as possible. Also, the action always starts in the first space all the way to the left. Using the "Back to the Future" example, the action for that first scene might read: "A myriad of CLOCKS hang against the wall. Each second hand in perfect precision with the other." All objects, character names and things of importance are capitalized.
Add the characters' names and dialogue to the script. Beneath the action, the characters' names -- always in caps -- are placed in the center of the page. The dialogue is typed beneath the names. As characters speak back and forth, insert new character names on subsequent lines. Add action to the script as needed as per Step 3.
Continue telling your story. As each scene ends, repeat the pattern with a slug line, action, character and dialogue until the story is complete.