Keep a journal of ideas. Every good film narrative starts as an idea in someone's mind. Keep your journal with you everywhere you go, and write down any ideas that come to your head. You can even keep your journal next to your bed for those times that you have a weird or crazy dream and need to write it down before you forget it in the morning.
Choose an idea and flesh it out. Once you have an idea that you like, start fleshing it out with details, and develop it into a plot line. What kind of characters would be involved with this idea? What would their careers be? What culture are they from? What personality do they have? All of these ideas will help you to create your narrative.
Choose the main conflict. Now that you have the idea and the basic ideas of the characters involved with this idea, create a problem or conflict that those characters need to solve. Is something lost? Has someone died? Narratives thrive on conflict.
Choose a resolution to the conflict. Of course, for every conflict you will need a resolution (except in some horror or suspense narratives). Write down how your characters are going to resolve the conflicts you have chosen and how they will be changed because of those conflicts.
Make an outline or time line of how your narrative will progress from start to finish. Having a time line will guide what has happened and what will happen to keep your story straight. Without a time line, when you start to actually write your finished product into your word processor, you could end up with a story that jumps or does not make sense.
Write your final product on your word processor. Take all your outlines and planning, and put them into the computer as text. Let your imagination run as you picture each scene in your head, and write what you see or hear. What are your characters saying? What does the environment around them look and feel like? Before you know it, you will have a finished narrative that you can show off to your family, friends or professionals.