When you write a case study you are taking the reader on a journey. It's the journey that you took in creating the case study in the first place. The more interesting you can make that journey the better will be your case study. You don't want to make it easy. You don't want to make the case study simply a list of facts or information which the reader absorbs from beginning to end without ever having to stretch their imagination. Take your reader on a mysterious tour.
It's most important that you do some research on the topic of your case study to make sure that you do not regurgitate what has gone before. It might be the same person or topic at the centre of your case study but you don't have to tackle the issue in the same way. Whatever the topic or issue of your case study you need to find a unique approach to it, one which will both interest the reader and which has not been covered before.
There are all types of research you can undertake to create your case study but one of the best is to be able to talk to people who were involved in your topic. If it's about a place or an event, then talking to a person or people who have been to this place or were involved in the event will give you a personal and unique insight into what you are to write about. You can always find information in printed material and online but to be able to actually talk to somebody who has firsthand experience is an ideal situation.
Once you have obtained considerable information about the theme or topic of your case study, your next test is the analysis. Not all information will be relevant. Some facts will be super important. Get your analysis skills to sort the information and place it in order of priority. You want to write well but you need the best and relevant facts to write about.
When it comes to the actual writing of your case study, you need to look on it as a film script, as a storyboard. Each aspect of your writing leads to the next. You build the case. You hold the reader's interest by not revealing your hand until the very end.