Contrary to what you might have heard, one does not insert a comma into a sentence simply because one pauses to take a breath while reading it.

1.       Use a comma before a coordinating conjunction when it joins two independent clauses. The coordinating conjunctions are for, and, nor, but, or, yet, so.

The weather was rainy, and I was running late for work.

Do not use a comma before a coordinating conjunction when it joins two words, two phrases, or two dependent clauses.

Janis and Frank are going hiking. (Two nouns)

At the beach, we lay in the sun for an hour and played in the ocean for three. (Two verb phrases)

When you think about it, you will know that John really loves you and that he is sincere. (Two dependent clauses)

2.       Use a comma after a subordinate clause when it begins a sentence. However, when a dependent clause comes at the end of the sentence, you do not ordinarily need a comma.

While Marilyn pushed the stalled car, her boyfriend watched.

Her boyfriend watched while Marilyn pushed the stalled car.

3.       Use commas to set off an adjective clause if the clause is not essential to the meaning of the sentence.

Mr. Hendricks, who lives on the corner of Elm Street, is an unusual person.

The old man who lives on the corner of Elm Street is an unusual person.

4.       Use a comma or commas to set off most conjunctive adverbs and phrases like however, for example, on the other hand, nevertheless, moreover, particularly, especially, therefore, and consequently.

Children learn to read, however, in spite of poor teaching.

I agree that is what should been done. However, I cannot bring myself to do it.

Note: If the conjunctions are linking two independent clauses, use a semicolon before the conjunction and a comma after it.

Children learn to read; however, they often do so in spite of poor teaching.

5.       Use a comma or commas to set off an appositive (a word, phrase, or clause used as a noun that identifies or explains another noun or pronoun).

Those were the happiest days of my life, the days when I was young and foolish.

One of their neighbors, Mr. Otis Hardy, is a very mysterious person.

John likes to eat carbohydrates, especially wheat bread, fruits, and vegetables.

6.       Use commas between items in a series (three or more words, phrases, or clauses).

She bought grapes, blueberries, and bananas. (Nouns)

My cat likes to eat tuna, climb trees, and chase mice. (Infinitive phrases)

We went to Marge’s house, we took a dip in the pool, and then we ate brunch. (Independent clauses)

7.       Use a comma or commas with direct quotations.

The policeman said, “You were going well over the speed limit.”

“You were speeding,” said the policeman.

“You were speeding, “ said the policemen,” and I need to see your license.”

8.       Use a comma or commas to set off items in dates and addresses, but not ZIP codes.

I was born Monday, January 3, 1965, in Birmingham, Alabama.

My sister’s address is Apt. D, 123 Oak Avenue, Boston, Massachusetts 89001.

9.       Use a comma after an introductory phrase if the comma makes the meaning of the sentence clearer.

After eating, my dog and I set out to complete the long hike up the mountain.

In the wee hours of dawn, my mother sometimes hears strange noises in the attic.

10.   Use a comma or commas to set off words, phrases, or clauses if they clearly break the flow of the sentence.

Luther, please stop whatever you’re doing and help me clear the table.

My Aunt Elizabeth, known for her habit of chewing tobacco, will be 102 this May. 

Greg was totally honest about what he had done, not that I would have expected him to act any differently.