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 where to place quotation marks
Periods and commas go inside quotation marks, even if they aren’t part of the material being quoted. All other punctuation marks go outside the quotation marks, unless they are part of the material being quoted.
“Any further delay,” she said, “would result in a lawsuit.”
His latest story is titled “The Beginning of the End”; wouldn't a better title be “The End of the Beginning”?

3. 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.)

4. 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.


5. 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.
Semicolon: Only a third of Americans have a passport; the majority of Canadians have a passport.
Colon: Only a third of Americans have a passport: for most, foreign travel is either undesirable or unaffordable.

Source: The Punctuation Guide