Open your new Word document. Go into the "page layout" tab and click on the "size" option to change your page size. If you want to print on pages that will be the same size as a standard paperback book, click on the "more paper sizes" and change the page size to 7 3/8 inches by 5 inches. However, if you want to use standard-sized typing paper to submit your book to a publisher, change the page size to 8 1/2 inches by 11 inches.
Get into the habit of setting your margins before you start writing; realize that you can adjust them at the end, if you wish. Click on the "margins" tab in the "page layout" menu and select "custom margins" to set a margin of 1 inch for all margins --- left, right, top and bottom. Expand on the left and right margins, if you wish to see more white at the sides, as publishers like to see plenty of white on the page, and a wider margin is useful for making editorial notes. Use this measurement for either submitting a book to a publisher or self-publishing. Check the publisher's guidelines concerning their specifications regarding the width of the left margin to accommodate the binding.
Use a font, such as Courier or Times New Roman, so that the text is clean, crisp and easily readable. Do not use fonts which are faint when printed like Arial or Verdana. Never use comic or ornate fonts for a book format with text, as they do not meet the industry standard. Type your manuscript, using double-spacing with a 12-point size font.
Center the title of the book in the header of the page. Set the pagination to appear in the center of the footer on each page --- with the exception of the title page, copyright page and blank pages.
Save your work as a PDF file, so that you can self-publish an eBook or submit the PDF file directly to a publisher.
You can also print your manuscript, using quality ink-jet paper, and submit the final hard copies of your book manuscript to a publisher. Ideally, these copies should be camera ready, so that the publisher can shoot and print directly from these copies.