Ben Yagoda on the use of the comma:
You see this kind of thing all over the Internet as well. People punctuate that way because, if they spoke these sentences, they’d pause after the conjunction (and because the extremely fanciful and undependable Microsoft Word grammar and style checker refrains from applying a squiggly green underline).
I'm no writer. I'm sure I get this wrong all the time. In fact, I know I do. (See what I did just then?) I do exactly as Yagoda suggests. I write commas based on how I would say or read the sentence.
He goes on about the use of the Oxford comma as well. Which I wholeheartedly agree with and strive to do myself though I'm sure if someone ripped through the catacombs of this here blog they'd find a million grievances.
Yagoda has a follow-up coming. Stay tuned.