Estimate the length of your short film. This length will help you pace your script. Each page of the script is roughly one minute of screen time. So if your short film is around 30 minutes long, the script should be 25 to 40 pages.
Use screenwriting software like Final Draft or Movie Magic Screenwriting. This will help with the spacing, formatting and margins. Always type screenplays in a Courier New font, the default font found in these screenwriting programs.
Introduce each scene with scene headings. As preproduction moves along, the scene headings become crucial in planning locations for shooting. A scene heading lists whether it is interior or exterior, the actual location and day or night. For example: “INT. BASEMENT—NIGHT” is a proper scene heading. Always use all capitals.
Write out action using concise, present-tense words. Write out everything the viewer would see on screen. For example: “The dog runs across the yard and jumps over the fence.” Avoid using “running” and “jumping.”
Add dialogue to scenes by centering the text, capitalizing the name, pressing enter and then typing the dialogue. Add any specific emotions next to the character name in parentheses, but usually it is the actor that chooses how to speak the lines.
Create montages by writing a scene heading and then using lines of action with two dashes. For example a running montage would look like this: “—Joe ties his shoes.—Joe runs down the road.—Joe wipes sweat off his forehead.” Press enter between each line to indicate a new shot and set-up.
Read your screenplay out loud to listen for mistakes. This will also help with dialogue.