By now, your brief should explain the business problem, the people involved, the outcome you need and the constraints around the work.
That is a much stronger starting point than a list of ads, pages and posts.
Use the downloadable Agency Brief Workbook below to bring those decisions together. It covers the questions explored in this series and leaves space for what you do not yet know.
Complete it with the people who understand the customer and the business. Where answers conflict, discuss them. Where evidence is missing, say so. You do not need to fill every gap before contacting an agency.
Then work through the brief together. Ask the agency what it would challenge, what it needs to investigate and whether the requested deliverables are the best way to achieve your objective.
Agree the working version before production begins. Revisit it when something material changes.
The value of the brief lies in the decisions it helps you make. Those decisions can reduce wasted effort and give the work a clearer chance of improving the business.