Use a comma between items that are listed in a series, which contain three or more words or clauses.
Example: We went to a movie, ate dinner and then went to a party.
Example: I bought a chocolate cake, strawberry pie and some ice cream for the party.
Use a comma when quoting the words of others.
Example: Michele grabbed her keys and said, “I won’t be back.”
Example: “Don’t hit your sister,” my mother warned.
Use a comma when writing dates and addresses.
Example: My address is 1234 Fake Lane Drive, Chula Vista, CA 91910.
Example: We are going to Ireland on May 25, 2012.
Use a comma after introductory phrases.
Example: Despite the fact that we haven’t spoken in weeks, I still sent Heather a gift for her birthday.
Example: After washing my hands, I cut the cake.
Use a comma before a coordinating conjunction when it joins two independent clauses. Coordinating conjunctions include for, and, nor, but, or, yet, and so. Remember, independent clauses are two complete sentences.
Example: The weather was rainy, and it was very cold.
Example: The girls overslept, so they did not go to school.
Use a comma after a subordinate/dependent clause when it begins a sentence. Subordinate/dependent clauses begin with words like if, because, after, when, as, while, since, even though, although, before, and whenever.
Example: While I ate my sandwich, my brother played. (Dependent clause is at the start of the sentence, so a comma is needed.)
Example: My brother played while I ate my sandwich. (Dependent clause is second, so no comma is needed.)
Use a comma to set off an adjective clause if it is not essential to the meaning of the sentence. Adjective clauses usually start with words like that, which or who.
Example: My uncle, who lives in Santa Barbara, loves to surf.
Example: The college, which is in El Cajon, is very nice.
Use a common when using conjunctive adverbs.
Conjunctive adverbs are words like however, on the other hand, although, nevertheless, consequently, therefore, especially, moreover, and for example .
Example: The Chargers looked like they were going to make it to the Super Bowl, however, I decided to root for the Cowboys.
Example: I decided to ask for a raise and, consequently, I was fired.
Use a comma to break up the flow of a sentence.
Example: Michelle, clean up your room!
Example: The entire congregation, known for their generous giving, donated money to build a new parking lot.
Use a comma to set off an appositive word or phrase that is used to describe or identify another noun.
Example: That was the best day of my life, the day when my daughter was born. (“Day” is repeated and is described further after the comma).