The more you get right in your manuscript before submitting to editors, the less work they'll have to do on mechanical issues—and the more time they can spend on making your writing shine. Plus, learning the conventions of fiction style* can save you money.
*This is Articulate Editing house style, which is based on generally accepted fiction conventions (in the US) and a pinch of personal opinion. Most of what is written here will apply across the board. If a guideline has wiggle room, I'll let you know. And if you're working with a publisher, make sure you follow their specifications, as their house style may differ slightly. (This style guide also applies to creative nonfiction.)
Titles of works
Most proper names don't require any special treatment besides capitalization. This includes names of restaurants, businesses, brands, cars, wars, churches, and museums. But titles of works and some types of names require italics or quotation marks.
Use headline style capitalization for titles of works. For more info on headline style, see my fiction style guide on capitalization.
Italicize titles of stand-alone works. For example, books, journals, movies, paintings, musicals, TV shows, record albums, comic strips, and book--length poems.
"What's your favorite episode of Game of Thrones?"
Beowulf is considered one of the most important epic poems in the English language.
Use quotation marks for shorter works or subsections of a larger work. For example, songs, most poems, chapter titles, episodes of TV shows, blog posts, and journal articles.
She put on Janis Joplin's Pearl album because she was dying to hear "Me and Bobby McGee."
"Do Not Go Gentle into that Good Night" is one of my favorite poems.
Ancient works of art with unknown creators are set in roman. (And don't require quotation marks, either.)
the Artemision Bronze
Venus de Milo
Works of art that are monuments are often set in roman.
the Statue of Liberty
Names of ships and other vessels
Italicize names of vessels such as ships, submarines, and spacecraft. (And capitalize.) When an abbreviation precedes the name, the abbreviation is not italicized.
the space shuttle Challenger
Other vehicle names, including aircraft, are capitalized but not italicized.
Herbie the Love Bug
Italics have a number of important uses besides setting off titles. The general guideline, however, is to avoid overusing optional italics, since italicized writing can be difficult to read.
When punctuation directly follows an italicized word, the punctuation should match the surrounding text unless the punctuation belongs to an italicized title. This is also true of boldface, and is true when reversed. (If the surrounding text is italics and a word was set in roman for emphasis, following punctuation would be in italics.)
Who took my copy of To the Lighthouse? (question mark belongs to surrounding sentence and is set in roman)
Who's Afraid of Virginia Woolf? (question mark belongs to title and is italicized)
Italicize unfamiliar foreign words that don't appear in an English dictionary ... maybe. While this is still listed as a rule in many style guides, it's a rule in flux. Doing so "others" speakers of non-English languages, and writers may have compelling reasons for not wanting to italicize non-English words in their work. There's a balanced and informative article on italicizing foreign words in fiction at CMOS Shoptalk. And for more on italicizing foreign words in dialogue, see my fiction style guide on dialogue.
Use italics for mottoes in any language other than English. Capitalize only the first word of the motto (sentence-style capitalization). For mottos in English, see below.
The college I attended had the motto Christo et regno ejus.
Italicize the Latin species names for plants and animals. A species name consists of both the genus and the species. Capitalize the genus and lowercase the species. Capitalize the genus even when used alone. Don't italicize the other taxonomic classifications such as family or order.
Chaparral dodder, Latin name Cascuta californica, looks like orange silly string.
There are several species of dodder in the genus Cascuta.
Italicize words that stand in for sounds.
He heard a tap, tap, tap on the window.
Crack! I turned and Sarah had fallen through the ice.
But ... if the word is used as a common noun rather than a representation of the sound, no need to italicize.
He heard a tap on the window.
Italicize words as words. When a word isn't used functionally but is instead referred to as a word, italics or quotation marks are both acceptable. Italics are usually preferred, but quotation marks sometimes work better to convey the idea of speech.
The word sad doesn't even begin to describe what I'm feeling.
My little sister says "hospital" as "hosbadiddle."
When proper nouns are used as words, set in roman.
When you write the word 7-Up in a novel, don't spell out the seven.
Italicize letters as letters. To prevent confusion, the plurals of lowercase letters are formed by adding 's (in roman).
the letter g
All the lowercase l's were actually uppercase i's.
"Put your X on the line."
In these two common expressions, the letters are set in roman:
Mind your p's and q's.
Dot your i's and cross your t's.
Academic grades are set in roman type. (And capitalized.) Plurals of capital letters don't take apostrophes.
He got mostly As and Bs, but his brother got all Cs.*
*I personally find this hard to read (my brain sees the word as, the abbreviation for bullshit, and the symbol for the chemical element Cesium), so if it were my book, I might want to use apostrophes. The reasoning behind no apostrophes is that the plural form isn't as confusing as it is with lowercase letters and that apostrophes are meant to be used for possessives. I say, if you can make an exception for lowercase letters, why not for uppercase?
Letters representing shapes are set in roman type. (And capitalized).
His feet were so big he looked like an L.
Letters standing for musical notes are set in roman type. (And capitalized).
the key of E-flat major
Creative use of italics
Use italics to emphasize a word or phrase, not boldface or all caps. (An exception being certain books for kids). Using italics for emphasis is sometimes discouraged; for my defense of the use of italics in fiction, see this earlier blogpost.
Italics are one way to set off a character's thoughts or telepathic communication. For more, see my fiction style guide on internal discourse.
Well, that's strange, she thought.
Italics can be used to differentiate a passage of text, such as a letter or a dream.
Except for dialogue, quotation marks in fiction should be reserved for words or phrases used ironically, or words or phrases quoted directly. For more on quotation marks, check out my fiction style guide on dialogue and my fiction guide on internal discourse.
"Scare Quotes" are used to alert the reader that something is being said ironically, is contrary to what the speaker really means, or is not the speaker's words. This is different than the emphasis italics imparts.
I "misplaced" that horrible sweater she knit me.
Don't use quotation marks to set off clichés. The speaker/narrator may be using figurative language, but they're still being straightforward.
That man Tony has "nerves of steel." X
If the common saying is a direct quote, do use quotation marks.
"Well, my dear, just like Mark Twain, I 'never let my schooling interfere with my education.' "
Use single quotation marks to set off text inside dialogue or a quotation as in the example directly above. This is the only time you would use single quotation marks in fiction writing (in American English). For more detail, go to my fiction style guide on dialogue.
When you write "so--called" before a word or phrase, you don't need to set off the following word or phrase with scare quotes unless you need to single out one word of a phrase.
Your so-called friend just told me not to invite you.
His so-called 'happy' dance is anything but to me.
Set long signs and notices off by quotation marks, with only the first word capitalized.
The door was marked "Trespassers will be shot and survivors will be shot again."
Short signs or notices are capitalized headline style and set in roman. Some publishers set these in small caps instead.
She saw a For Sale sign on the lawn.
Mottos are treated the same way as signs. (Unless they're in a foreign language, in which case they're italicized and the first word is capitalized as above).