Use commas to separate items in a list
Use a comma before a coordinating conjunction in a compound sentence
Use commas after introductory words, phrases, or clauses
Use commas to set off nonessential information
Use commas to separate direct address
Use commas with dates, addresses, and place names
Use commas to separate quoted material from dialogue tags
Use commas in numbers with four or more digits
Use commas to separate coordinate adjectives
Use commas in salutations and closings of letters