Grammar: Commas

Several years ago I worked with someone who, though otherwise quite intelligent, had only a tenuous grasp of the rules of English grammar. Someone had told her that people didn't use commas enough, so she started inserted commas everywhere in her writing. The fist sentence in this post might look like this:
Several years ago, I worked with someone, who, though otherwise, quite intelligent, had only a tenuous grasp, of the rules of English grammar. 
While it's probably true that the comma is underutilized, it's also possible to overutilize it.

The basic mistake that many people make with respect to commas is that you don't use them every time there would be a pause if what you are writing is being spoken aloud. In short, a comma is used to separate parts of a sentence from one another. Here are a few ways that a comma should be used correctly:

• Before a coordinating conjunction (and, but, or so, yet) that links two independent clauses (an independent clause has both a subject and a verb and can stand on its own as a sentence). For example "I went running, and I saw a duck". If the sentence is changed to "I went running and saw a duck" no comma is needed because the second half is not an independent clause. 
• After a dependent clause that starts a sentence (a dependent clause has a subject and a verb, but cannot stand on its own), as in the sentence "When I went running, I saw a duck". If the dependent clause is at the end of the sentence a comma is not needed, but can be added for emphasis. 
• Use commas to offset explanatory, but unnecessary, information in the middle of a sentence. "When I went running I saw a mallard, a type of duck". "A type of duck is explanatory, but the sentence can stand without it.
• To set off items in a series. There is some disagreement about whether a comma follows the last item in the series (called an Oxford Comma) is necessary, however, more often than not it clarifies the situation. "When I went running I saw some ducks, Charlie, and Bill." This obviously tells us that I saw some ducks, but also saw Charlie and Bill. "When I went running I saw some ducks, Charlie and Bill." This version of sentence could mean that the ducks that I saw were named Charlie & Bill. 

The following link gives nine more examples of the proper use of commas. 

http://www.businessinsider.com/a-guide-to-proper-comma-use-2013-9

And this link simplifies it all into three rules.

http://www.writewithjean.com/usage-and-grammar/commas-made-simple/

That's a lot of rules. I try to narrow it down to:

1. Use a comma in a list of items
2. Use a comma to separate different ideas or thoughts within a sentence. 
3. Don't use it to indicate a pause or a breath.