Many new writers will sit down to a blank page, type in the title to the book they want to write and then type "Introduction". They sit there, starting, trying to figure out how they are going to write the introduction to the book they haven't even written yet.
Write Your Outline First
If you haven't written the outline for your book yet, now is the time to do it. Writing a basic outline for a nonfiction book is not difficult. The more times you do it, the easier it will get until you reach the point where you can outline an entire book in under an hour.
Write Your Chapters
After you have completed an outline, begin working on the chapters. I like to work on my chapters in the order I have them written, but I have read of other writers who work on whatever chapter or section they feel like tackling. Find your own method for writing your chapters and perfect your method.
Edit First Draft
After you have finished writing your book, go back over it a second time. Reread everything and make first round edits. When you do this, you refresh your memory on what you have already written. You can make notes on the key points you go over and use these to write your introduction.
Write the Book's Introduction
After you have written your book and gone through the first edit, you are now well versed in what you have written. Now is the time to write your introduction and mention the key points covered in your book.