That's right. 12 panels. These panels will serve as the barebones structure of your story. The following breakdown is roughly based on Joseph Campbell's mythical structure and Christopher Vogler's Hero's Journey. Add captions, thought balloons, or bits of dialogue to support the images.
- Panel 1: The Setup. Draw the "World," in which your story will take place. In that world, draw your main character doing what he normally does in that world.
- Panel 2: The Inciting Incident or Call to Adventure. In this panel, draw the situation that prompts the main character into contemplating his main objective. This is where the "ultimate goal" is first described.
- Panel 3: The Doubt. In this panel, draw the circumstance that would make your main character initially refuse to take action.
- Panel 4: The Decision. In this panel, draw a situation that ultimately compels the main character to pursue the objective.
- Panel 5: The Subplot, or the "B" story. In this panel, draw another situation that isn't directly connected to the main objective, but wherein your main character is also involved.
- Panel 6: Getting Ready. In this panel, draw the main character preparing for the "journey" ahead.
- Panel 7: First Major Obstacle. In this panel, draw the main character encountering the first major obstacle.
- Panel 8: Second Major Obstacle. In this panel, draw the main character encountering the second major obstacle.
- Panel 9: The Chasm. In this panel, draw a situation wherein the main character begins to believe that all is lost and failure is inevitable.
- Panel 10: Objective Level-Up. In this panel, draw the Subplot (depicted in panel 5) getting drawn into or influencing the main character's quest. The main character's goal takes on a different meaning.
- Panel 11: The Final Battle. In this panel, draw the main character encountering the big-daddy obstacle to his goal.
- Panel 12: The Denouement. The end thought. The main character, triumphant or otherwise, realizes something at the end of his journey.
Phase 5: Panels to Pages
When you're done with your 12 panels, you can begin to add some story details by expanding each panel into a page. Page one is an expansion of the Setup panel. Page two is an expansion of the Inciting Incident panel. And so forth. The result is a 12-page story which may still not be completely threshed out, but it keeps your story within the original idea. As you convert panels to pages, you might find the need to change or adjust or add more depth to some story details, and that's fine. You're still doing 12 pages anyway.
Phase 6: Expand As Necessary
You can expand your 12-page story as you see fit. Maybe you need to expand the first page (Setup) to eight, and the second page (Inciting Incident) to five. Your First Obstacle page might need 15 to twenty. You might even think of doing the expanding in full script form or the "Marvel-style" description method, with the 12 pages as your guide. It's here where you begin to think about pacing, nuance, styling, and all the little but juicy good stuff. What's important at this point is the confidence you have in the 12-page story.
This is, of course, very very basic, and those who are interested in knowing more about storycrafting only need to do further research.