If there is one piece of punctuation that gives people pause more than any other, it would have to be the comma. The comma is the most over-used and most often incorrectly used form of punctuation. Although it can be tempting to throw commas around willy-nilly, it is best to show a bit of restraint. Commas are the perfect little helper when it comes to separating clutter, but the last thing you want to do is to allow that silly comma to do just the opposite and clutter your work needlessly. It is time to get a grip on the comma and put it in its place — and nowhere else.
The most obvious time to use a comma is when separating the items in a list. An important point to note, however, is that the comma preceding the conjunction at the end of the list, the serial or Oxford comma, is not necessary.
When combined with conjunctions, commas are used to separate two independent clauses, meaning that if the two parts can stand alone as complete sentences, then a comma must be used. However, if the two parts do not form complete sentences, then a comma is a no-no. Although it is always tempting to toss in a comma before a conjunction like “but” or “and,” it is not always necessary.
A comma must also be used A) in front of or around information that modifies the subject and B) following an introductory phrase at the beginning of the sentence.
A) I really want that coat, the one that Tom is wearing.
The coat I got from Tom, the red one with the patches, is far too big for me.
B) When you go to town tomorrow, pick up a new coat for Tom.
One of the trickiest situations when deciding whether or not to use a comma is with two or more adjectives that describe a noun. If the two adjectives carry the same weight in describing the noun, and their order is reversible without modifying the meaning, then they require a comma.
There are many specific rules for comma usage with words like “as,” “while” and “since” that need to be accessed on a case-by-case basis. Knowing when and when not to use a comma takes practice. When in doubt, a writer is always served well by turning to their style guide of choice for help. Brush up on the basics, and prepare to do battle with the elusive comma.