Helpful Hints in the Use of Commas
Tina Miller, MA,CFLE stashed this in writers
What follows is not a comprehensive guide to the many uses of commas, but a quick tour of the most common errors involving them.The first thing to note is that the comma often marks a brief pause in the flow of a sentence, and helpfully marks off one phrase from another. If you write “I plan to see Shirley and Fred will go shopping while we visit” your readers are naturally going to think the announced visit will be to both Shirley and Fred until the second half surprises them into realizing that Fred is not involved in this visit at all. A simple comma makes everything clear: “I plan to see Shirley, and Fred will go shopping while we visit.” People who read and write little have trouble with commas if they deal with English primarily as a spoken language, where emphasis and rhythm mark out phrases. It takes a conscious effort to translate the rhythm of a sentence into writing using punctuation
Rule of thumb: Use as few commas as possible.