Everyone and their brother has an opinion about how to use commas.
It's the Swiss Army knife of punctuation—good for (almost) every use.
A traditional rule is to use a comma whenever you'd naturally pause in a sentence, but we're not really traditional-type people. And you know what? There isn't really a standard. Some publications, like The New York Times, use commas like they're going out of style; other publications, like US Weekly, sometimes forget they exist.
The one thing that all of these writing pros have in common? Consistency. Commas may be a party, but they aren't confetti. You can't just throw them as you please. Once you know (and judge) the rules, you can use them as you'd like—as long as you keep it consistent.
Here are the basic rule of when to use commas:
1. To separate the words in a series or list.
My grocery list included vanilla extract, pickles, and Frosted Flakes.
2. Before the coordinating conjunction (remember the FANBOYS!) when forming a compound sentence
Vance wanted to stay up late to watch King Kong, but he fell asleep at 8:30.
3. To separate a dependent clause from an independent clause when the dependent clause comes first.
If she finished her homework early, Lee would have time to play Call of Duty.
4. To set off introductory words, phrases, and clauses.
Sadly, we had to cancel our vacation to Dollywood.
5. To set off parenthetical elements like appositives, interrupters, and adjective clauses that aren't essential to the sentence's meaning.
My dentist, Dr. Cordula P. Willifarth, says I need to floss more often.
Randy, of course, is running late again.
Karen, who has a long history of kleptomaniac behavior, stole her neighbor's riding lawn mower and drove it to Wisconsin.
6. To separate dates and place names.
Oslo, Norway, is home to many mischievous trolls.
December 7, 1941, is a date that will live in infamy.
7. After the greeting in a friendly letter/email, and after the closing in all letters/emails.
Dear Uncle Phil,
Sincerely,
8. To set off nouns in direct address.
Jack, your feet smell awful.
I told you, Tina, we have to pick up the tickets at the box office.
9. To set off direct quotations in a sentence.
"The Rangers game starts at 6:30," said Alan.
The girl behind the counter asked, "Do you want fries with that?"
10. To set off interjections.
No, you can't have a pony for Christmas.
11. To separate adjectives of equal importance.
The tall, handsome man walking toward them had to be an undercover cop.
12. In numbers of more than three digits.
1,999 22,566 525,600