Read over the script, story or other source material to get a feel for how the story is told. The picture card story should reflect the action in the story, with each new index card representing a new course of action.
Draw out what your characters are doing at the opening of the story or scene and show how or if they are moving. Label this card "#1" to show the beginning of the sequence.
Add in any dialogue, if needed, that is necessary to understand the panel without rehashing entire conversations from the script. Only include the dialogue necessary for this particular panel or card.
Add in any notes, such as camera directions, by using arrows to express movement or writing notes below the drawing.
Draw your second card to show any passage of time from the card before it, as needed. For example, card 1 may show a man walking toward a door, while card 2 shows only a hand turning a doorknob. The viewer of your cards should be able to connect that very little time has passed and the hand on the knob belongs to the man in card 1.
Number the next card accordingly and add in new dialogue, if needed, as well as directional arrows for movement and/or necessary notes. Continue to draw subsequent cards to tell the story visually until you reach the end.