The comma is one of these pesky little punctuation marks that seems to trip up a lot of people in terms of its usage. There are eight essential rules of comma usage, and most of them you probably already know (even if you don't know the technical grammar rule behind them). Pay particular attention to rules 3, 4, and 5 as those are the most common comma errors I see.
Rule #1 Use commas to separate items in a series of three or more things.
Example: I bought cookies, cake, and pizza at Publix this afternoon.
NB: The final comma is considered optional and referred to as the Oxford comma (sometimes called the serial comma). In my very grammar-snobbish opinion, this should not be optional.
Rule #2 Use a comma between two independent clauses that are joined with a coordinating conjunction (FANBOYS)
Example: My dog chased three rabbits out of the woods, but they all got away.
Rule #3 Use a comma to separate subordinate (dependent) clauses at the beginning of sentences.
Example: Because I haven't done my English assignment, I'm now failing the class.
Before eating three candy bars, I should have thought about the consequences.
Rule #4 Use commas to set off interrupters: clauses, participial phrases, appositives, or other nonessential information.
Example: Barrack Obama, the former President of the United States, might have a 4th of July hot dog eating contest at the White House.
Lebron James, as you can see in this video here, dominates all his opponents.
Rule #5 Use a comma to separate a quotation from the rest of the sentence.
Example: "Please do your homework," my teacher begged.
My teacher begged, "Please do your homework!"
"Please do your homework," my teacher begged, "or you will not pass your class!"
NB: Punctuation always goes inside quotation marks.
Rule #6 Use commas after introductory words or mild interjections.
Example: Yes, I am unrealistic.
Unfortunately, you must learn the rules of English grammar.
Rule #7 Use a comma to separate a noun of direct address.
Example: Let's eat, Grandma.
2.02 Assessment
Complete the 2.02 Comma Rules worksheet and submit for grading.