Analyze your script. Depending on how hands-on you are, you may storyboard key moments of the film, a few shots per scene, or every single camera motion. Any of these is fine and varies widely from director to director. Sit down with the script and find the scenes that are most important to you and to the story. Focus on them first, and use them as your jumping-off point. Draw notes in the margins or keep notes separately on a pad, noting scene and page numbers.
Picture the shots. Before you take any further steps, you should make sure that you have a clear vision of what each shot will look like. This will help you communicate it clearly. Think of how you would explain the shot to someone else, how it will look through the camera, how it will look to the audience and how it will look to you, watching it from the outside. This is part of the previsualization process, or "previz," which determines how the film will look. The process often also includes production design, lighting design and costuming.
Determine your medium. Director Ridley Scott draws tiny pencil drawings that his crew calls Ridleygrams at the moment of shooting. This is all the storyboarding he ever does. Other directors use what is called an animatic, coverting storyboards to digital images, making an initial version of the movie with stick figures and vague shapes that can be watched. This can be used later to make sure that every shot is perfect. Whether you choose to create slides in PowerPoint or make tiny stick-figure drawings on file cards, the rules are the same and you can do as much or as little as you like.
Create your storyboards. The most important thing is to make sure that your storyboards require no explanation at all. This will take some practice, but by using the basic principles of comics, speech bubbles and movement lines, you should be able to tell the story of your film just with your storyboards. Others involved in the film should be able to immediately understand what is going on and what their jobs will be.
Share your storyboards. Film is a collaborative medium, and storyboards are one of the great ways to make sure everyone involved understands your vision. Take the time before you shoot to make sure that everyone is on the same page and understands what you want. Make any necessary adjustments to your storyboards before shooting.