Character profile worksheet. If you want to go deeper with your characters, you'll need a full dossier describing their physical appearance, manner of speaking, behavioral traits, and background. From their hair color to their biggest secret, this questionnaire covers it all.
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.