Snowflake method checklist. Maybe you'd rather work from the top down than from the ground up. Inspired by fractal geometry (really!), Randy Ingermanson's "snowflake method" grows an entire novel from a single sentence. Each step of the process methodically expands upon the one before, filling in detail until you have a complete draft.
Story beats template. Adapted from the world of screenwriting, this popular method replaces the concept of acts with a set of milestones that commonly appear in many kinds of stories. Hitting these "beats" gives your story a rhythm while leaving the details open to your imagination.