Here are five pieces of my best advice:
1. Use styles for all distinct formatting instead of using direct
formatting. E.g., chapter titles, headings, body text, etc. That way, if you
ever need to change the formatting, you can modify the styles to change
everything of a certain kind all at once, rather than having to look for
places that need to be changed and applying different direct formatting.
In addition, if you use Heading 1, Heading 2, etc. for chapter and heading
titles, and you later want to reorganize the book in any way, you'll be able
to do it in Outlining mode, which makes moving huge sections of text child's
play.
2. Don't use manual page breaks at all until the document is ready to be
printed. In the end, you will need to use them seldom, if ever. But, if you
get into the habit of trying to make things align as you go along, you'll
drive yourself nuts trying to fix the formatting each time something is
inserted or deleted.
3. Word can handle 250 to 300 page books quite readily. Many others will
tell you this. However, over 20 years of experience with every version of
Word ever released has taught me that big = risky. When I work on books,
large government reports, etc., I break the document up into chapters or
sections. This not only reduces the chances of document corruption, but it
also makes working with each section a lot faster. If I'm writing a book for
a publisher, the chapter files remain separated. I never put them together.
When I'm going to be doing the printing myself or need to turn something
over to a client, I put things together only at the last minute.
4. If you need to use cross references, use the facilities built into Word.
For example, if you refer to figure 3-4, use fields to do it, rather than
typing the numbers directly. If you insert, remove, or move figures around,
the numbering can be updated by updating the field codes. This is a lot
easier than having to go through an manually renumber figures and references
to them.
5. Enable both backups and AutoRecover. And save often. When you answer the
phone, press Ctrl+S. When you get up to get some coffee, press Ctrl+S. When
you're preparing to do something different to the document, press Ctrl+S.
When you hear the sound of thunder, press Ctrl+S.
Good luck!