When I first tried to create a case study, I committed one of the sins of UX writing: sharing too much information.
A case study is supposed to show potential employers and clients that you know your stuff. Every flow I've worked on has a back story, and I want to share that experience with the intended audience. That means giving the information in a simplified way, a snapshot of your process. It doesn't mean writing down every single step along the way.
I've learned that case study reviewers are usually looking for a few things:
That you know how to write
You don't have to (and actually shouldn't) showcase your most creative, quirky copy. Reviewers want to see that you know how to communicate information in the most concise and clear way possible. Good UX writing doesn't try to be noticed; the focus of your case study isn't just the copy; it's how the copy solves a problem.
That you can tell a story
Every good story has a beginning, middle and end. A couple of mismatched screenshots of your work isn't going to make much of an impression. Focus on a specific flow, and on what specific challenges you faced along the way.
That you know the process
Writing isn't just about tapping on a keyboard. It often involves research, meetings, trial and error, testing, iterations, debate, compromise, and more. Your case study should provide clear reasons for the decisions you made, and prove that you're able to stand by your work.
That you work well with others
Nothing happens in a vacuum. Did you work along PMs, designers, and analysts? Did different stakeholders hold different priorities? Offer a glimpse into that back-and-forth. You can also touch briefly on other stages of the process that you had a hand in, like localization or research. Even though we think of writing as a solitary job, UX writing is anything but.
If you're looking for your first UX writing job, or just trying to get better at UX writing, I wish you the best of luck. It's a process that often feels like an uphill battle, but the learning curve becomes less steep over time. Check out some of my example case studies in my Portfolio, and follow the blog for more UX writing tips.