My Grammar and I (Or Should That Be 'Me'?): Old-School Ways to Sharpen Your English

So where does a comma go?
‘We spent most of our time sitting on the back porch watching the cows
playing Scrabble and reading.’
A comma can go in lots of places. Here are seventeen – count ’em – examples:
  1.   At a place in a sentence where you wish your readers to pause:
Take a breather, will you?
  2.   After introductory words or phrases that come before the main clause:
In 1066, the English lost the Battle of Hastings.
Once upon a time, there lived a boy called Jack.
Of course, …/However, …/Finally, …/Yes, …
  3. Between separate clauses within a sentence:
In the beginning, when God created the universe, the earth was formless and
desolate.
  4.   Before direct speech:
He asked, ‘Can you tell me why I should take any notice of these rules?’
   5.     In  addresses  and  place  names  where  one  part  of  the  place  name  gives
further information about the other:
Ye Olde Cottage, Old Ford Road, Fordcombe.
The President was assassinated by a gunman in Dallas, Texas (as  opposed
to any other Dallas).

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  6.   On  either  side  of  parenthetical  phrases  or  clauses  (those  non-restrictive
bits  that  contain  extraneous  information,  see
here
).  These  are  known  as
paired or parenthetical commas, so there must always be two of them:
She reversed into the bollard, which she could have sworn was not there an
hour before, causing considerable damage to her car.
One  day  in  the  near  future,  if  we  can  believe  what  scientists  tell  us,  this
planet will run out of oxygen.
  7.   After items in a list:
My  favourite  Victorian  novelists  are  the  Brontë  sisters,  Wilkie  Collins,
Charles Dickens and Thomas Hardy.
In American English there would also be a comma after Charles Dickens  ;
British English does not generally think this is necessary.