If you are writing a non-fiction book, you might want to try a writing method I learned from Author/Marketer/Self-Publisher/Consultant Fred Gleeck. He calls it 'The 24x4x2 Method'.
The basic idea is to break down book into small enough pieces that you can then easily create. You start by creating a list of 25 major topic headings for your subject.
Once you have a solid list of 25 major topics, you go through that list and create 4 sub-topics for each major topic.
Finally, you write 2 pages for each of the sub-topics you identified. Then, write an introduction for each of your 25 major topics that introduces the four sub-topics.
When you're done, you'll have a roughly 200 page book draft written.
You can create the 2 pages for each sub-topic in any way you want - write it out longhand, type it at the computer, dictate it into a recorder and have the recording transcribed, or hire a ghostwriter.
Andrew