Decide how you want to outline. The index card method has been around for decades. It's simple and effective because you can keep your outline in front of you at all times. If you have a cork board in your office, you can pin your index cards to the cork board and rearrange them as you outline. There are also software programs available, such as Movie Outline, aimed at making the outline process easier. If you use screenwriting software like Final Draft or Movie Magic Screenwriter, these programs have outline tools built in. Regardless of the method you choose, the process of outlining remains the same.
Decide whether you want to do a scene outline or a step outline. A scene outline is much less detailed. Write a scene heading on the front of your index card, at the top. Write the heading as you would in your screenplay. For example, INT. HOTEL - NIGHT. Beneath the scene heading, write an overview of the scene. The overview should be a short description of the action that takes place in the scene, touching on any major plot point or twists. Also include a note about anything in the scene that must happen to set up another scene in the movie. Turn the card over and write the names of the characters that appear in the scene. Include any notes about character behavior in this section as well.
Expand your scene outline by stapling additional index cards to the main scene cards they relate to. During the course of writing a movie, you will need to cross reference scenes, or even small actions within a scene, to other scenes in the movie. These are events that must happen to ensure another scene or action in the movie makes sense. Write these actions individually and attach them to the scene index card in which they happen, then indicate the scene you want to relate the information to in a parenthetical note. This allows you to track the continuity of your story. These individual steps should be more detailed than the main scene card. Write down exactly what the characters do and how it ties in with the referenced scene.
Arrange your cards under a general three-act structure to help you pace your movie. The three-act structure is the most basic structure used for the movies. A two hour movie is about 120 pages. The first 30 pages is act one, the middle 60 are act two, and the final 30 make up the third act. Hang a three-act timeline on your cork board and pin your scene cards beneath the act they fall under to help you determine whether or not your scenes occur where they should in the overall structure of the script.