Page Setup for Paperback-Sized Pages
A typical Word document, in 11-point font, allows you about 630 words per page (17 words across the page and 37 lines down the page). A typical paperback usally has only about 400 words per page, with much narrower margins (allowing only 10-12 words per line, 32-38 lines per page).
To set up a Word document in a simaler format, set margins for 2.1" (in all directions), keeping the font at a standard 12 pt. New Times Roman. This yields 10-12 words per line, 35 lines per page, about 370 words per page with justified alignment.