Good interior layout is invisible: readers never consciously notice fonts, margins, or spacing when they're done well, but they absolutely notice when something's off. These basics won't turn a manuscript into a design showcase, but they'll keep formatting from distracting from the writing.
This is part of the Complete Guide to Book Cover Design and Interior Layout.
For body text, readability matters far more than personality. Serif fonts (with small decorative strokes at the ends of letters) are the traditional choice for long-form print reading and remain the most common choice in fiction and nonfiction alike, since the serifs are thought to help guide the eye along a line of text. Sans-serif fonts (without those strokes) are more common in certain nonfiction categories, and are the default on most e-readers regardless of what font you choose, since many devices let readers override it.
Whatever you choose, stick to one body font throughout, and reserve display fonts (more decorative or stylized) for chapter titles and headings only, never for body text.
Body text is typically set between 10 and 12 points for print, adjusted based on the specific font (some read larger or smaller than their point size suggests). Line spacing (the space between lines) should be comfortable without looking sparse; too tight feels cramped, too loose feels like the page is trying to pad out a short manuscript.
Print margins need room on every edge, and the inside margin (nearest the spine) typically needs to be slightly larger than the others to account for the book's binding, so text doesn't disappear into the gutter when the book is opened. Margins that are too narrow make a page feel crowded and can cause practical problems with binding; margins that are too wide waste space and can make a manuscript look artificially padded.
Chapters conventionally start partway down the page, not at the very top, giving the reader a visual cue that something new is beginning. Chapter numbers or titles are usually set in a distinct style from the body text, consistent throughout the book. Many print books also start each new chapter on a fresh page (sometimes specifically a right-hand page), which is a formatting choice worth deciding on early and applying consistently.
Fiction and much nonfiction use indented paragraphs with no extra space between them, rather than block paragraphs with a blank line in between (which reads more like a web page or business document than a book). The first paragraph after a chapter heading or scene break is conventionally not indented. Consistency matters more than which specific convention you choose.
Within a chapter, scene breaks (a shift in time, place, or point of view) need a visual signal, commonly extra white space, a centered symbol or ornament, or both. Without a clear signal, readers can lose track of a transition that was intended to be immediate.
Print books typically include running headers (often alternating the book title and current chapter title or author name on facing pages) and page numbers, usually positioned consistently throughout. These should be unobtrusive; readers should be able to ignore them entirely unless they're specifically looking for a page number.
A widow is a single line of a paragraph left alone at the top of a page; an orphan is a single line left alone at the bottom. Both look like formatting mistakes and are typically fixed by hand during a careful layout pass, adjusting spacing or breaks slightly so paragraphs don't split awkwardly across pages.
Individually, none of these choices is dramatic. What actually signals professional layout is consistency: the same font, size, and spacing decisions applied the same way throughout the entire book, with no unexplained variation from chapter to chapter. Inconsistency, more than any single wrong choice, is what makes a layout feel amateurish.
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