Start with reliability
A prompt is not a magic line of text. It is an instruction you expect a model to follow again and again, even when users type messy input.
For a hackathon project, your prompt must survive real demo use. A judge should see the same kind of useful output on different cases, not one lucky answer.
One idea
A prompt holds up when it makes the job testable. It says what to do, who it is for, what not to do, and how you will know the answer is good.