These comma rules come from my high school English teacher.
Comma Rules by Mike Cullinan
C-1. Prevents confusion, especially reading aloud. (Behind, the car was a mess)
C-2. Joins two sentences with a coordinating conjunction. (eg – and, but, or, nor, for, so, yet)
C-3. Placed within series of three or more; put the comma BEFORE last in series. (Our flag’s colors are red, white, and blue.)
C-4. Placed between coordinate consecutive adjectives modifying same noun. (She is a poised, elegant, gracious lady.)
C-5. Follows introductory dependent clauses. (When you have finished, you may leave.)
C-6. Follows introductory phrases. (Stopped by a frustrated Sancho, Don Quixote decided to rest.)
C-7. Follows transition/connecting words or phrases. (furthermore, in consequence, therefore, indeed, and so forth.)
C-8. Sets off parenthetic elements NOT ESSENTIAL to the sentence. (therefore, I hope, naturally, in the first place, by the way, after all, of course, on the other hand)
C-9. Sets off non-essential modifiers: clauses, phrases, appositives. (John Smith, Jr.)
C-10. Sets off expressions of contrast. (Tom, not Fred, brought the candy.)
C-11. Indicates understood words or the omission of words. (She went skiing; I, skating.)
C-12. Sets off short direct quotations, dialogue, and so forth. (Keats said, “Let’s go sailing.”)
C-13. Sets off direct address. (Boys, here it is.)
C-14. Sets off a mild interjection or exclamation from the beginning of the sentence. (Ah, I guess so. Yes, he can go.)
C-15. Sets off an echo question. (It is good, isn’t it?)
C-16. Placed between duplicate words used for effect. (Methuselah went slowly, slowly down the mountain and was very, very careful not to break his old, old bones.)
C-17. Sets off year when using month, day, and year in dates. (April 21, 1989, was a good day.)
C-18. Sets off elements in an address except state and zip. (Austin, Texas, is a great place to visit.)
C-19. In letters, sets off an official title following a name when both are on the same line. (John Adams, President), follows complimentary closes (Sincerely, Cordially, Yours truly, ), and follows an informal salutation (Dear Igor, Dear Friends).
C-20. In numbers, follow a consistent pattern of usage.