In the standard format, section text is double-spaced, left-aligned, and set in a 12-point Courier font. The first line of a paragraph is indented one half inch, or 5 characters, from the margin. The margins are set so that there are 25 lines per page, with each line having a maximum of 60 characters.
Why is that? So that your editor can estimate the word count and accurately determine the final page count of your book. The math works like this: Sixty characters per line at an average of six characters per word (a publishing industry rule of thumb) works out to an average of ten words per line. A 25 line page, then, will have an average of 250 words--a nice big round number. Four pages is about a thousand words. Four hundred pages is about a hundred thousand words. By the way, the first page of a chapter is estimated to have 250 words, and partial pages other than the first page are estimated to have 125 words.
Section breaks (the visual breaks between the scenes in your story) are indicated using a centered number sign (#). Don't use a blank line to separate your sections since it is easily missed by the typesetter.
Page headers typically include your last name, followed by your novel title (which you can shorten if you have a long title), and end with the page number.
Chapters begin on a new page about a third of the way down and start with a centered chapter title, usually in all caps (i.e., all of the letters are capitalized).
When you send your manuscript to agents and editors, you'll want to include a title page to let people know how to contact you and where to send the checks. You can use the title page template in the Notebook as a starting point.
Type your name, address, phone number, and email address in the upper left corner in single-spaced, 12-point Courier. In the upper right, type the word count. Calculate the word count using the estimating method outlined on page 2 (and round up to the nearest thousand) rather than using the actual word count calculated by the program.
Center your novel's title about halfway down the page, add two single-spaced returns, and then your name (or pseudonym) as you want it to appear when your book is published.
That's about it.
[Note: Storyist's Novel template provides styles that implement these formatting guidelines.]