Here are the notes I use, any time I realize that the idea in my head isn't a fully developed plot.
1. Hook: Starting state of hero, generally opposite of the end state (who, what, where, when)
2. Plot Turn 1: The conflict is introduced
3. Pinch 1: Apply pressure and force the hero into action
4. Midpoint: Where hero starts moving from reaction to action, starts progressing toward end state
5. Pinch 2: Why the resolution is difficult; the hero's low point, back against the wall
6. Plot Turn 2: Hero gets the last piece of the puzzle necessary to solve the problem
7. Resolution: Climax, not denouement