Commas: They're Not Just For English Majors Anymore.
FIVE RULES TO COMMA GLORY
By Joseph Sigalas, Ph.D.

source: (http://crosswaterfarm.com/commas)

Don't Forget!: 
 YOU MUST HAVE A REASON FOR EACH COMMA YOU USE.

IE - Introductory Elements
An introductory element is a word, phrase, or clause before the main part of the sentence. It usually tells us something about the main clause.

If we cannot control our tempers, we may have to bite those mimes.

On the other hand, they may bite us first.

CE - Contrasting Elements
Use commas to set up a strong contrast.  Some key words: but, yet, not, never, although 21C - Two Independent Clauses
(a.k.a. "compound sentences") When two independent clauses are joined with a coordinating (and not any other kind of) conjunction, place a comma before the conjunction. (Remember the FANBOYS: for, and, nor, but, or, yet, so) CA - Compound (or Coordinate) Adjectives
Use commas to separate consecutive adjectives: Do not, however, use a comma when the order of the adjectives matters (i.e., when you can't simply reverse them without seriously changing the meaning):
We were suspicious of the fried green tomatoes.
(Fried green tomatoes may taste good, but green fried tomatoes might make you sick).  OR, try inserting and between the adjectives.  If and works without changing the meaning, use a comma. If and doesn't work, don't use a comma.
We were suspicious of the fried and green tomatoes.
This sentence says that some tomatoes were fried, while others were green.  That's not the same as "fried green tomatoes," so don't use a comma.

NRE - Non-Restrictive Elements
These elements are the ones known, often misleadingly, as "the part you could just take out": parenthetical comments, direct address, appositives, transitional words and phrases, etc.

They can also appear at the end of a sentence:
He begged to run into the airplane propeller, an act which would have dramatically shortened his life expectancy.

The clowns were scary, especially the sarcastic ones.

Two other situations you probably already know:
 
1) items in a series (more than two items)
  • When listing items in a series (more than two items), do not place a comma after the last item.
      South Park, Sponge Bob, and 60 Minutes are my grandmother's favorite shows.
  • Placing a comma after the penultimate item is optional, but sometimes necessary for clarity.
      confusing: Jenny has worked for many gun manufacturers, including Browning, Winchester and Smith and Wesson.

      clear: Jenny has worked for many major gun manufacturers, including Browning, Winchester, and Smith and Wesson.

    The comma in the second example makes clear that Winchester is distinct from Smith and Wesson.
2) interjections and direct address
Whoa, dude, that's radical.
Special Case: Commas With Quotations and Other Punctutation

Here are four tips:

1) Use commas to set quotes off from the words used to introduce or identify the source.

The cartoonist shouted, "I quit!"
2) Do NOT use a comma, however, when the sentence includes MORE THAN the quote and the words used to
    introduce it:
The cartoonist sang "I love myself" before she left for beauty school.

The satisfied man wrote "This restaurant stinks" on a napkin and had it sent to the cook.

3) Do NOT use a comma when a quotation is introduced by "that."

4) When a quotation is part of an introductory or other type of clause requiring a comma, place the comma INSIDE
    the quotation marks. In written American English, commas (and while we're at it, periods too) never go outside the quotation marks -- no matter how much you want them to.

    Wrong:
      When the nutty captain shouted "Pancakes for everyone", the crew went crazy for joy.


      My favorite song is "I Love You, You Love Me", but I haven't told anyone yet.

Right:

When the nutty captain shouted "Pancakes for everyone," the crew went crazy for joy.

My favorite song is "I Love You, You Love Me," but I haven't told anyone yet.

© 2000-2008 Joseph Sigalas / revised 03/2008