Where you did this · Your role
Start with the situation. What existed before you got involved? What team or company was this for? Give just enough context that someone outside the company can follow.
Then the problem. What wasn't working? What were people struggling with? Be specific. Vague problems make for vague case studies.
Then what you did. This is the part that matters most. Walk through the key decisions, not just the deliverables. What did you try? What did you rule out? What tradeoffs did you make? People want to see how you think, not just what you shipped.
Then what happened. Did it work? What changed? Numbers are great if you have them. If you don't, describe the impact in concrete terms.
Optional: what you'd do differently next time. This is the part people remember. It shows self-awareness and it's usually the most interesting thing you can say about a project.
Delete all of this and write your own. Or keep the structure and just replace each section.