Plan Draft Revise is the secret to writing fast.
If you're a Planner, you map out your whole story before writing a single word. You clothe the outline in narrative, revise the structure top-down, and then polish the wording. As long as you resist the impulse to compose and edit at the same time, you'll write faster.
But what about Pantsers, those writers who write by the seat of their pants? Half of all writers plunge in without knowing...