Break down your screenplay into shots. "Shots" are the unit of uninterrupted film that are edited together to make a scene. A feature-length screenplay may have hundreds or thousands of individual shots. It has been said that the shower scene in Hitchcock's movie, Psycho, contained about 77 camera angle and 50 cuts in the 3-minute scene.
Evaluate each shot. Ask yourself where the shot takes place, who or what will be in it, what purpose it serves, what kind of shot -- such as close-up, wide angle or establishing -- it will be, what angle it will be from, what movement -- of subjects or of the camera itself -- will take place in it and how it will transition into the next shot.
Make a list of shots and decide which shots will be storyboarded. While every shot does not need a storyboard, it is a good idea to storyboard the entire film anyway, especially if you are a beginner or if you're going for a special artistic effect through out the entire film, like low-angle shots or noir lighting. At the very least, however, you should storyboard those shots that will require special planning, such as action, special effects or particularly artistic shots.
Print or create empty storyboard panels. The medium you are shooting for affects the kind you need: TV storyboard panels are square; theatrical panels are rectangular. Many websites, such as animationmeat.com/templates/templates have both kinds of panels available for free download. Storyboard panels should have lines underneath them for text that explains the drawing.
Draw the shot. Every director and storyboard artist works differently: some draw richly detailed graphic novels, others draw simple sketches. Whichever method you prefer, your drawing must be drawn from the desired camera angle, and include all actors and significant props in the scene with arrows to indicate both their movement and the camera's movement. Use shading to indicate lighting if important to the scene. Include the shot number either in a corner of the storyboard box or in the description lines underneath.
Write a general description of what is happening in the shot on the description lines to clarify the drawing.