Rule#1: USe commas in compound sentences when clauses are separated by a conjunction such as "and," "but," "for," "nor," or "yet."
a) I wanted to go to class yesterday, but I wanted to take a nap more.
b) She did not respond to my email yet, but hopefully she will today.
Rule #2 Use Commas to separate elements in a series. Such elements usually are adjectives, verbs, or nouns.
a) Her new boyfriend is tall, dark, and handsome.
b) Bob, Joe, Greg and Ryan dug a big hole.
Rule#3 Use commas when attributing from quoted material.
a) He said, "Hello," and then promptly left.
b) I told her she didn't need to yell, but she kept screaming, "go clean your room."
Rul#4 Commas follow introductory matter.
a) When the horn sounded, they knew half time was over.
b) If we were to build a really big bonfire, how much wood would we need?
Rule#5 Commas follow the salutation of a friendly letter and the complimentary close of any letter.
a) and b)
Dear Darla,
I hate your stinking guts. You make me vomit. You are scum between my toes.
Love,
Alfalfa
-The Little Rascals :-D
Rule #6 Commas follow all items in a date or full address
a) On January 14, 1988, she had her first child.
b) I have wanted to live in Boston, Mass., for as long as I can remember.
Rule #7 Commas surround nonessential words or phrases.
a) As a matter of fact, I would love a peanut butter and jelly sandwich.
b) However, I would like strawberry, not grape, jam on the sandwich.
Rule#8 Commas surround words of direct address
a) Alyssa, did you buy milk today?
b) Obviously, Steve, you are not impressed.
Rule #9 Commas indicate omitted verbs, usually expressed in another part of the sentence.
a) They went searching for buried treasure; rum they found.
b) She couldn't dance to save her life; ice skating is a different story.