Chicago Manual of Style devotes 16 pages to the correct usage of the comma. I’m sure you’re familiar with its use with coordinate adjectives, transitional adverbs, appositive clauses, and participial phrases. I won’t insult you by repeating that information here. Instead, here are the most common errors in comma usage spotted around the Web.
Omitting a comma after city and state
When writing the name of a city followed by its state, most writers know to include the comma between the two, but often overlook the comma that’s required after the state name. Here’s how to punctuate a city, state combo correctly:
He knew he was washed up in Bath, Maine, when his show was scrubbed.
Show me the St. Louis, Missouri, map.
Omitting a comma after city and country
When writing a city name followed by the country See More . . .