Define one purpose
Name the person or team the role supports and the output it prepares. 'Marketing assistant' is too broad. 'Turns approved customer interviews into first-draft case studies for the marketing owner' is testable.
Specify inputs and sources
List the approved material and its order of authority. Tell the assistant what changes quickly, what must be checked every time and what it should do when sources conflict.
Write an output contract
Define the fields, structure, reader, maximum useful length and final control block. Require assumptions, sources and outstanding checks to be visible.
Separate preparation from authority
Allow summarising, organising, comparing and drafting. Require human approval for money, contracts, people decisions, sensitive customers, public claims, regulated matters and irreversible actions.
Test three real examples
Use an ordinary case, a messy case and a high-consequence edge case. Record correction time and the reason for each correction. Improve a reusable instruction only when the same failure could happen again.