we should write a novel here.
this is the novel.
generally, once you're inside a novel, you are introduced to a character who is doing something. the arc of that gesture is an allegory for who that character is, and provides the jump-off point for filling in enough of a past to give what follows a certain weight and/or structure.
for making something fast, i would think exquisite corpse might be a good procedure:
Exquisite Corpse
you could say that what is required is an initial gesture, or you could say that this is the initial gesture, that we are already inside, and that there's no way to go but forward since time is not reversible.