Ground
Agree what the work is for, and look at the real data.
We write a one-page Decision Brief. It names the decision the work should improve, the person who owns that decision, how we will measure the result, and what it is worth. At the same time we profile the actual source data, draft data contracts with the people who own each source, and write down the security and compliance rules that apply, so they shape the design from the start.
