ref – http://www.brainfuse.com/curriculumupload//1185318888766.html

Put a comma between independent clauses of equal value when there are three or more, and they themselves don’t have commas in them.

Form: First independent clause, second independent clause, and third independent clause.

An independent clause is a group of words containing a subject and a verb that could stand alone as a sentence. If your sentence contains multiple independent clauses, separate them with commas.

Example:

Aliens was a great movie, the people loved its originality, and I’m sure there will be more fans in the future.

Put a comma in front of a coordinating conjunction to join two independent clauses in a compound sentence.

Form: Independent clause, [conjunction] independent clause.

Example: I wanted to go swimming today, but the weather had other ideas.

Note: You don’t need a comma if the clauses are very short.

Example: You pitch and I’ll catch.

Do not put a comma in a compound verb. Use a comma only if the second verb has its own subject.

Example (no comma): David loves computers and got a job as a computer artist.

Example (with comma): David loves computers, and he got a job as a computer artist.

Put a comma after a dependent clause that comes before an independent clause in a complex sentence.

Do not put a comma if the independent clause comes first.

A dependent clause is a group of words containing a subject and verb that can’t stand alone as a complete sentence. A dependent clause typically begins with words like after, although, because, if, since when, while, etc.

Form: Dependent clause, independent clause.

Example: Whenever I see a rainbow, I think about my favorite movie.

Form: Independent clause dependent clause.

Example: I think about my favorite movie whenever I see a rainbow.

Put a comma between two adjectives–

1. when they describe the same noun, and

2. the word “and” could be put between the adjectives without changing the meaning.

Example (with comma): the fat, colorful parrot (fat and colorful parrot)

Do not use a comma between two adjectives if the second adjective and the noun go together as one item. If the word “and” doesn’t sound right between the adjectives, leave the comma out.

Example (no comma): white wedding gown

Use a comma to separate three or more items in a series.

Example: Pa bought potatoes, peaches, and peppers.

*Some writers don’t put a comma in front of the conjunction before the last item in the series. This is known as the Oxford comma, and while its use is becoming more popular, it’s still considered an optional addition.