Name the context honestly
Label a fictional brief as fictional on the first page. If you use real work, obtain permission and remove confidential information. Describe your own contribution rather than implying that you owned an entire campaign.
Present the reasoning
State the business question and the evidence available at the time. Explain what you considered, what you chose and why. Include the limitations that could change the interpretation.
A simple structure works: context, observation, hypothesis, action proposed, measurement and reflection. Use the search lab as practice material, not as a claimed client result.
Separate proposal from outcome
If a change was never implemented, call it a proposal. If a result was measured, explain the time period, definition and constraints. Do not invent spend, sales, clients or return figures to make a case study look complete.
Make the next conversation easier
Keep the main story short and make supporting calculations readable. Ask a reviewer what information is missing before polishing the visual presentation. A clear unanswered question can demonstrate care.