What is the best way to write a book using Microsoft Word?

How your book is formatted in Word primarily depends on the size of your finished book. Industry standard sizes vary and you will first want to select the size of your book with your publisher. Once the physical book size is selected you can format your Word document page to reflect this in the Page Layout Settings. Then you can set your margins, e.g. .25 on all sides and .5 on the interior pages. There are a myriad of helpful videos and templates available through a quick google search. Remember to check with your publisher as well, because most publishers will have a template for you to download and use with all this already set.