Punctuation Rules for Comma Use

Rule 1. To avoid confusion, use commas to separate words and word groups with a series of three or more.
Example: My $10 million estate is to be split among my husband, daughter, son, and nephew. Omitting the comma after son would indicate that the son and nephew would have to split one-third of the estate.
Rule 2. Use a comma to separate two adjectives when the word and can be inserted between them.
Examples: He is a strong, healthy man.
We stayed at an expensive summer resort. You would not say expensive and summer resort, so no comma.
Rule 3. Use a comma when an -ly adjective is used with other adjectives.
NOTE: To test whether an -ly word is an adjective, see if it can be used alone with the noun. If it can, use the comma.
Examples: Felix was a lonely, young boy.
I get headaches in brightly lit rooms. Brightly is not an adjective because it cannot be used alone with rooms; therefore, no comma is used between brightly and lit.
Rule 4. Use commas before or surrounding the name or title of a person directly addressed.
Examples: Will you, Aisha, do that assignment for me?
Yes, Doctor, I will.
NOTE: Capitalize a title when directly addressing someone.

Source: http://www.grammarbook.com/punctuation/commas.asp