Use commas to separate elements in a series, but do not put a comma before the conjunction
in a simple series.
ie. The flag is red, white and blue.
ie. He would nominate Tom, Dick or Harry.
Put a comma before the concluding conjunction in a series, however, if an integral
element of the series requires a conjunction.
ie. I had orange juice, toast, and ham and eggs for breakfast.
Use a comma also before the concluding conjunction in a complex series of phrases.
ie. The main points to consider are whether the athletes are skillful enough to compete, whether they have the stamina to endure the training, and whether they have the proper mental attitude.