The basics
There are two rules you should follow:
Use the tried-and-tested structure
A typical case study flows like this: Problem → Solution → Results.
Your first describe the problem the client was facing (or the business goal they wanted to achieve), then you describe how you helped solve that problem, then you show what results the client got after you solved said problem for them.
Tell a story
Case studies are called customer stories for a reason.
Take the reader through a “hero’s journey.” Craft a narrative of how everything transpired. One thing led to the next. That way.
People don’t want to read a mundane account of everything that happened in the project, they want to read an interesting story.