By Natalie Bright
Put a comma:
Before—and, but, or, for, nor, yet, still, when joining independent clauses.
He arrived in town last August, and everyone was happy to see him again.
Between—all terms in a series, including the last two.
She brought candy, cookies, and punch to the meeting.
To set off—parenthetical openers and afterthoughts.
Running to meet him, the children helped him carry the books into the house.
Before and after—parenthetical insertions (use a pair of commas).
He, overjoyed at their greetings, hurried toward the villagers.