We all have areas in life we would like to learn more about. Some of us have goals to learn a foreign language, play piano or learn how to juggle. There could be more obscure subjects you want to find information about but can’t. Or, you can find some information, but it is really out of date. It is time for you to write about what you need or want to learn.
Can’t find a book on a subject you’re interested in? Write one! You’re not an expert? Who cares! Write from research and by the time you finish your book you will then be an expert on that subject. What book would you like to exist? If it doesn’t exist and you would buy it – write it! Sure it is better to already be an expert, but the plus side of writing from a beginner’s point of view is you are offering a fresh outlook on the subject.
Experts might skip over areas that a beginner won’t. You are writing from the beginner’s point of view and it is likely you will both have the same types of questions. What do you want to know? What do you want to know more about but can’t find information on it? Choose a subject you know little about but are very interested in.