When reading, I’ve noticed that most people leave out the final comma when separating three or more words in a series. In looking up the rule online, I have found that the final comma is always used. There is an interesting article on the subject that can be found online
When you take a college proofreading class, you will find that the comma in a series includes the word before the conjunction. The Gregg Reference Manual, used in one such college proofreading class, states:
When two or more items are listed in a series and the last item is preceded by and, or, or nor, place a comma before the conjunction as well as between the other items.
Many people, however, leave this comma out. This...