Setting up your data team for success starts with proper requirements.
It starts with a top down design methodology. Understand the business process, document it, maybe create a conceptual model and the relationships that are involved so that you can articulate it back to the business stakeholders.
Bill Inmon, the godfather of data warehousing, proposes a top-down approach to understand the business process.
Understand the Business Process
You will need to understand the process being modeled from the business perspective. The goal is to gather enough information from the business stakeholders that you can create a conceptual model to review with them.
Build a Business Glossary
Documenting business terminology serves many purposes.
What Data Sources will you be loading?