As an editor, the most common punctuation issues I see are with comma usage. Writers can avoid many comma pitfalls by mastering the conventions below.

1. A comma is placed before a coordinating conjunction (for, and, nor, but, or, yet, so) that connects two independent clauses (complete sentences).

• Incorrect: Suzanne wants to attend the writing seminar and Nancy wants to go shopping.
• Correct: Suzanne wants to attend the writing seminar, and Nancy wants to go shopping.

2. Comma splice—a comma isn’t strong enough to connect two independent clauses.

• Incorrect: Nicholas rode his bike to the park, Jordan took the bus to the library.
• Correct: Nicholas rode his bike to the park, and Jordan took the bus to the library.
• Correct: Nicholas rode his bike to the park. Jordan took the bus to the library.

3. Introductory words, phrases, and clauses are followed by a comma.

• Incorrect: Before leaving for her trip Patti will have her car serviced.
• Correct: Before leaving for her trip, Patti will have her car serviced.

4. Nonessential information (also referred to as a nonrestrictive clause or parenthetical element is set off with commas.

A nonrestrictive clause adds extra detail and can be removed from a sentence without changing the meaning or losing the identifying/distinguishing fact.

• Incorrect: Mary Brown who is an avid reader has worked at the local bookstore for fifteen years.
• Correct: Mary Brown, who is an avid reader, has worked at the local bookstore for fifteen years.