As an editor I sometimes wonder at the excessive use of commas. This form of punctuation was never meant to be inserted any time a writer feels the urge. It has many proper uses, and there are actually rules that apply.
The Comma Splice: This is a pet peeve of mine. When a writer joins two complete sentences together (independent clauses) with nothing more than a comma, this is incorrect. The proper form of punctuation in this instance would be the semicolon.
Wrong: John walked to the front door and rang the bell, he left quickly after getting no reply.
Correct: John walked to the front door and rang the bell; he left quickly after getting no reply.
Commas and Quotation Marks: In addition to writing it, I edit a fair amount of fiction, and one of the mistakes I commonly find is the placement of commas outside quotation marks in dialogue.
Wrong: “I can’t wait to meet him”, said Alice.
Correct: “I can’t wait to meet him,” said Alice.
Coordinating Conjunctions: Unless one or both sentences is quite short, use a comma before a coordinating conjunction (and, but, or) when joining two independent clauses (i.e., two complete sentences).
Example: Margaret truly had a desire to make new friends, but she just couldn’t imagine herself going to the networking event.
Appositives: I’m positively nuts about appositives! As long as the information in the appositive is non-essential to the meaning of the sentence, it’s proper to place commas around the appositive in the middle of a sentence.
Example: The green-cheeked Amazon, a type of parrot, enjoyed sitting quietly on his perch as he watched the song birds out the window.
Introductory Dependent Clauses: It’s proper to place a comma after an introductory dependent clause.
Example: When Janet walked by the ocean, she always felt a sense of serenity and calm.
Commas to Address: When addressing someone, add a comma to offset the name of the person.
Example: Darlene, are you able to help me?
Offsetting the Negative: When you want to negate something in a sentence by adding a “not” statement, use a comma to do so.
Example: The green-cheeked Amazon is a type of parrot, not a parrotlet.
The Oxford Comma: Using the Oxford comma before the words “and” or “or” in a list has become the subject of much debate. I minored in journalism during college, and in that training the Oxford comma was strongly discouraged. However, it was the norm in literature classes. Which is correct? These days either is acceptable. Sometimes including the Oxford comma actually helps the sentence make sense. I personally would vote in favor of this old school usage, but I’m perfectly fine as an editor if a writer prefers to omit this comma.
Example of an Oxford comma: She planned to wear either the pink, yellow, or blue dress to the party.
Option 2: She planned to wear either the pink, yellow or blue dress to the party.
These are just a handful of the rules regarding commas. Get a good reference book and look up any additional questions.