Aaron Sorkin, speaking of screen plays, said the first thing you must have is Intention & Obstacle. You have to know what your protagonist’s intention is and which obstacles will get in his/her way. The obstacle could be physical, or another character or an event; it doesn’t matter. He said I&O is the taught cable on which you can hang all your ‘writer stuff’. Without Intention & Obstacle, your story can’t support anything else. Hope this helps.