I spend some time upfront determining this based on the topic, judges, and my team. If you have a non-technical team, or it's a future tech hackathon (crypto, e

I spend some time upfront determining this based on the topic, judges, and my team. If you have a non-technical team, or it's a future tech hackathon (crypto, etc) you need to go for the big pie-in-the-sky ideas. If it's an industry competition (e.g., video compression APIs or something), you want to keep it small and technical.