Let’s start with something simple—serial Commas. Many authors have a strong opinion on this topic. I deal with serial commas—or the lack thereof—all the time when editing papers.
What Is a SERIAL COMMA?
A serial comma is the comma immediately before the coordinating conjunction in a series or list of three or more items.
Want an example?
“The daggers, helmet, and cloak belong to me.”
See that comma before the coordinating conjunction, “and”? That’s the serial comma in its natural environment, prowling the bush in search of its next meal. It is glorious isn't it? Yes, I am of the opinion that serial commas are glorious.
Now, here’s the deal. Serial commas are not required, they’re optional (depending on who you’re writing for. The New York Times for example has their writers leave out the serial comma to keep the punctuation light). But generally speaking in novel writing today, we use them, and we use them liberally. Why? Having that last comma there helps eliminate any ambiguity as to the relationship between the last two items in the list.
I saw a funny little flyer just the other day on Facebook showing the silliness of the omission of the serial comma that went something like this:
With serial comma,
“I had eggs, bacon, and milk.”
Without the serial comma,
“I had eggs, bacon and milk.”
Pretty silly, but it raises a point. You have a definite distinction with the serial comma where there’s room for ambiguity without it.
Regardless of which you choose to use—stick with that method. Don’t change halfway into a book or article. Either use the serial comma, or don’t. That’s the only wrong usage of the comma here; you must stay consistent with your usage of the serial comma.