With examples from Heroes, Stargate SG-1, and Doctor Who.
The use of single quotation marks mainly depends on the writer’s style. Single quotation marks are rarely used in the United States while in the United Kingdom single quotation marks are more often used interchangeably with double quotation marks, although even this is not a hard and fast national distinction and mainly depends upon the writer’s, editor’s, or publisher’s personal preference and style.
In the US style, single quotation marks are standard when quoting something within a quote.
Example: “My dad’s all, ‘I’m just trying to protect you,’ but he’s really just ruining my life,” Claire complained.
British usage would be opposite this: ‘And my dad’s all, “I’m just trying to protect you,” but he’s really just ruining my life,’ Claire complained.
Otherwise, there are no special rules in fiction writing that dictate the use of single quotation marks over double quotation marks. In some academic writing there are different conventions for when it’s appropriate to use single and when it’s appropriate to use double, but these vary from field to field so I won’t discuss the specifics here. What follows is a quick review of when it’s appropriate to use quotation marks in general in fiction writing.
Written Speech and Exact Quotation
The most common use of quotation marks is, obviously, around quotations. Quotation marks should always be used to set a character’s speech off from the actual narrative.
Example: Carter stopped short as the words sank in. "What did you say?" she asked O’Neill.
Quotation marks are also traditionally used around any direct quotation within a narrative, whether the passage is spoken or not, although this rule is more flexible depending upon the writer’s personal style. For example, if you have Jack O’Neill writing a mission report and you include the exact words he’s writing, those should be set off with quotation marks. If you have Daniel Jackson reading a book and you include an actual passage from what he’s reading, that should also be set off with quotation marks.
Quotation marks are used around the titles of works of art that are short such as short stories and poetry, or are a subset of a larger work such as book chapters, magazines/journal articles, album tracks, and television episodes.
Example: "Smith and Jones" is the first episode of the third series of Doctor Who.
Quotation marks are also often used for nicknames or false/ironic titles embedded in real names.
Example: Sam walked slowly through the SGC, building up the courage to tell Daniel "Give me caffeine or die" Jackson that the commissary was out of coffee.
Quotation marks are also used to signal unusual usage of a word, such as surrounding a word with what is known as ironic quotes or scare quotes to indicate a sarcastic usage.
Example: Martha Jones held on for dear life as the Doctor "landed" the TARDIS.
Quotation marks should probably not be used for word emphasis, because confusion may arise. For example, a reader may believe the writer is using scare quotes instead of quotations for emphasis, which would lead to a misunderstanding of the word’s intent. Underlining or italicizing would work better for emphasis.
Remember, single quotation marks can almost always be used interchangeably with double quotation marks, and both follow the same grammatical rules. Whether you use one or the other in your work will depend on your personal style. Whichever way you prefer, though, just be sure to keep your usage consistent. Pick a style and stick to it for the entire written piece.