Comma coma 101!

That little tail on the line causes so much angst to so many (me included).
According to Lynne Truss ("Eats, Shoots & Leaves" 2006), the earliest drill you should master when it comes to commas is:

1. in a list
2. before dialogue
3. to mark out additional information

This is backed up by Flesch and Lass (The Classic Guide to Better Writing -1996), who tell us:

1. Put commas between items in a series. eg I go to the movies by myself or with a friend or in a group.... I go to the movies by myself, or with a friend, or in a group.
   
2. Put commas where you want the reader to slow down. e.g. I had to sign for that special delivery letter with my feet bare and water running in the bathroom. (here the reader has a tendency to read I had to sign with my feet.) I had to sign for that special delivery letter, with my feet bare and water running in the bathroom.
   
3. Put commas after introductory phrases and clauses where you don't want the reader to run words together . e.g In short pants are practical garments.... In short, pants are practical garments. and.... When you were hammering grandma woke up. When you were hammering, grandma woke up.
4. Parenthetical expression - something wedged into the sentence that without it, the sentence would still make sense. eg... The landlord, paid promptly every month, was smiling.
5. Also Parenthetical expression - a direct address. eg. Dont' eat Henry until everyone is at the table... Don't eat, Henry, until everyone is at the table.
6. Then the trick one.... direct address or apposition depends on comma placement. eg Mike, the author of Hamlet, has been dead for over three hundred years. (we all know Mike didn't write Hamlet.) Mike, the author of Hamlet has been dead for over three hundred years.
7. Restrictive and non-restrictive clauses - placing the comma in the right spot makes a difference to the meaning. eg All the people in the auditorium who had had enough of classical music started to leave..... (some people will stay - restrictive) now read it All the people in the auditorium, who had had enough of classical music, started to leave. (Everyone leaves - nonrestrictive) In theory you can take out the words between the commas and it still makes sense.
   
8. Never use a comma instead of a period (stop). Use the stop when you want the reader to stop, drop their voice, and pause.
9. In the 'run-on sentence there is a comma where in fact it should be a stop. Save your reader the extra work... e.g. I was thinking about what Dad had told me, before I knew it the bus had passed our corner. Should be - I was thinking about what Dad told me. Before I knew it, the bus had passed the corner.
10. Conversely, in sentence fragments the writer puts stops where a comma should go. eg. 'Stopping to look at you. or Hoping to hear from you. ' Both need something more to make proper sense. "Stopping to look at you, I recognized you immediately. and Hoping to hear from you, Regards, Kathleen."
    

Hope this helps.