You'll have few problems with the comma if you understand these rules.
If you are listing only two items, use and or or. Do not add a comma.
Example: I brought chicken and bratwursts to the barbecue.
Put a comma around non-essential material and parenthetical expressions.
If the added thought, word, or expression is not essential to the main idea of the sentence, use commas.
Read the sentence without the added material. Does it make sense? Is the added information necessary to the idea of the sentence? If the information is not crucial to the reader's understanding, then set it off with commas.
Example: Mark, who is the loudest and most obnoxious guy at the college, is a good writer.
Put a comma around an interjection or afterthought that interrupts the flow of the sentence.
Again, use commas if you can read the sentence without the added material and if the information is not crucial to the reader's understanding.
Example: Well, I think she's coming to the party, isn't she?
Put a comma and a coordinating conjunction (and, but, or) between independent clauses.
Independent clauses can stand alone as sentences. They have an active subject and an active verb. If you do not add a comma between two independent clauses, you have created a run-on.
Example: Columbia has a lot of great restaurants, and its nightlife is fantastic.
Use a comma to set off introductory phrases and dependent clauses.
Dependent clauses cannot stand alone as sentences. They have a subject and a verb, but include subordinating conjunctions such as because, although, and since.
Example: Distracted by his cell phone, the man drove through a red light.
Example: Because she did not review her notes, she did poorly on the test.
Put a comma around words that would otherwise mislead the reader.
Without the comma in the following example, the reader may say, "Wait a minute! What ate the child?" Don't mislead your reader. Keep things clear.
Example: After eating, the child became sleepy.
Use a comma after a direct address to a person or a group of people.
Without the comma in the second example, it sounds as if the writer has the power to stop all children in the world from singing by only clapping her hands.
Example: Mary, would you like to have dinner with me?
Example: Children, stop singing when I clap my hands!
Do not separate the subject and the verb.
Do not separate the verb and the part of the sentence that completes the verb.