Get the body text right before you worry about the rest of the document.
The four most important typographic considerations for body text are point size, line spacing, line length, and font (see font recommendations).
Point size should be 10–12 points in printed documents.
Line spacing should be 120–145% of the point size.
The average line length should be 45–90 characters.
Page margins should be larger than one inch on 8.5″ × 11″ paper.
Avoid goofy fonts and monospaced fonts.
Avoid system fonts if you can.
Use curly quotation marks, not straight ones (see straight and curly quotes).
Use bold or italic as little as possible, and not together.
All caps are fine for less than one line of text.
Use centered text sparingly.
Put only one space between sentences.
Don’t use multiple word spaces or other white-space characters in a row.
Use 5–12% extra letterspacing with all caps and small caps.
Kerning should always be on.
Use first-line indents that are one to four times the point size of the text, or use 4–10 points of space between paragraphs. Don’t use both.
Always use hyphenation with justified text.
hyphens and dashes are different characters.
Use proper trademark and copyright symbols—not alphabetic approximations.
Put a nonbreaking space after paragraph and section marks.
Use a sequence of underscores to make a signature line.
Apostrophes point downward.