I always feel that anyone who can tell a story can certainly write a book but when it comes to writing a book in the non fiction category, things are different. You need to know what you are writing about and if you don’t, then you need to educate yourself.
That said, what area of non fiction do you want to write in? Some works of non fiction sell better than others and there is more interest and demand for certain categories of books. Of course if the intent is there to write on a certain topic, by all means do so, just try to do some research first to see how your book can stand out and competitively challenge other books and influence readers in their buying decisions.
Generally when writing a work of non fiction, it is easier to clearly define what the book is about and which keywords best represent the book from a search engine perspective.
With good planning, it should be easier for your book to be found online. This can be more difficult with works of fiction.
If your book is for offline retail, it will be in the specialty category for the type of work it represents. Make sure your book cover and description makes it clear where it belongs.
Assuming you have your topic selected to write about and are confident you can write a whole book on the subject-break it down into subtopics or chapters. Try to keep the flow of the book such, that each chapter makes sense in the order of the book. For example History and risk factors associated with PTSD, PTSD symptoms, coping strategies for PTSD sufferers, coping strategies for families etc.There is a natural order to how the book content progresses.
You can write a book outlining your hobby, things you have learned, for example, better ways of doing X,Y or Z that someone is actually interested in reading about, a problem solving type book, an educational book etc.
If you are a business owner, what problems keep coming up for your clients? Can you write a book about strategies you would implement so that you will be seen as an expert in your field? Hey presto you can use your book for promotional purposes too to build connections, get speaking engagements, build your client base, get more interest in your business or service or in you as a professional.
The only thing you really have to remember and be able to answer, is why is this important for the reader to know, what problem will this solve or what benefit will they gain? Answer this and then write your book with these questions in mind and go ahead and give readers what they want.