1. Use apostrophes correctly
Maybe it’s because of its diminutive size, but the apostrophe tends to be neglected and misused in equal measure.
The apostrophe is used to form possessives (e.g., the school’s faculty, our family’s crest, the shirt’s collar, Bill Thomas’s house) and certain contractions (e.g., it’s, let’s, she’s, they’re, I’ve, don’t).
The apostrophe is not used to form most plurals (e.g., she is looking at several schools, the families have similar crests, these shirts are on sale, we are dining with the Thomases). There are three exceptions: plurals of lowercase letters (e.g., dot your i’s and cross your t’s); plurals of certain words used as words (e.g., we need to tally the yes’s, no’s, and maybe’s); and plurals of certain abbreviations (e.g., the staff includes a dozen Ph.D.’s and four M.D.’s).
2. Know how to punctuate with parentheses
When a parenthetical element is included at the end of a larger sentence, the terminal punctuation for the larger sentence goes outside the closing parenthesis. When a parenthetical sentence exists on its own, the terminal punctuation goes inside the closing parenthesis.
She nonchalantly told us she would be spending her birthday in Venice (Italy, not California). (Unfortunately, we weren’t invited.)
3. Use a hyphen for compound adjectives
When two or more words collectively serve as an adjective before the word they are modifying, those words should normally be hyphenated. The major exception is when the first such word is an adverb ending in -ly.
The hastily arranged meeting came on the heels of less-than-stellar earnings.
4. Distinguish between the colon and the semicolon
The colon and the semicolon can both be used to connect two independent clauses. When the second clause expands on or explains the first, use a colon. When the clauses are merely related, but the second does not follow from the first, use a semicolon.
Only a third of Americans have a passport; the majority of Canadians have a passport.
Only a third of Americans have a passport: for most, foreign travel is either undesirable or unaffordable.
5. Avoid multiple punctuation at the end of a sentence
Never end a sentence with a question mark or exclamation point followed by a period. If a sentence ends with a period that is part of an abbreviation, do not add a second period.
I don’t particularly like the play Who’s Afraid of Virginia Woolf?
I didn’t like it even when I worked at Yahoo!
I especially didn’t like it when I saw it at 5:00 a.m.
6. Use a colon to introduce a list only when the introductory text is a complete sentence
Not all lists should be introduced with a colon. The general rule is that if the introductory text can stand as a grammatically complete sentence, use a colon; otherwise, do not.
Please bring the following items: a flashlight, a comfortable pair of hiking boots, and a jacket.
Please bring the typical evening hiking gear: a flashlight, a comfortable pair of hiking boots, and a jacket.
Please bring a flashlight, a comfortable pair of hiking boots, and a jacket.
Please bring: a flashlight, a comfortable pair of hiking boots, and a jacket.
7. Use commas to indicate nonessential information
If explanatory matter can be omitted without changing the general meaning of the sentence, it should be set off with commas. If the explanatory matter is essential to the meaning of the sentence, do not set it off with commas.
The novelist Don DeLillo seldom gives interviews.
The novelist, Don DeLillo, seldom gives interviews.
Explanation: The identity of the specific novelist is essential to the meaning of the sentence. Otherwise, there is nothing to indicate which of the multitude of novelists is being referred to.
America’s first president, George Washington, served from 1789 to 1797.
Explanation: America has only one first president. Identifying him by name is not essential to the meaning of the sentence.
America’s first president George Washington served from 1789 to 1797.
8. If in doubt, rewrite
The easiest way to solve a vexing punctuation problem is to avoid it. If you aren’t sure how to properly punctuate a sentence—or if the proper punctuation results in a convoluted, confusing, or inelegant sentence—rewrite it. Perhaps as more than one sentence.
Source: The Punctuation Guide. Reproduced for educational purposes.