I know this sounds hard but think about it.
— Ask yourself why you are interested in this subject and where have you found your information to get you feeling this way. Magazines, TV, internet, social groups, book, newspapers, seminars.
— Gather all your notes from any of these resources and start writing. You might be amazed at what you already know.
— Read over what you find, can you find more, better, is anything missing? Be like a detective dig and overload your mind with all the materials and eventually you will be the material and speak the material then you can write the material.
And then the resources become part of your book in the resources page.
Remember, do something every day toward your book and promotion.