Use double quotation marks — singles are only for “quotes within quotes”:

“I can sing ‘Twinkle, Twinkle, Little Star’ all by myself,” the little girl said.

What quote marks are for:

What quote marks are not for:

Emphasis. If you want a word or phrase to stand out, put it in bold, all caps, a larger font, a contrasting color or all of the above – NOT in quotes. (See what we did there?) There is a special place in Copy Crank Hell for those who misuse both quote marks and apostrophes as attention getters (“New Car’s” for sale! Don’t miss out on our “Big Deal’s”!).