Commas are used to connect:

• two dependent clauses

• an independent clause and a dependent clause 

Commas are NOT used to connect:

• two independent clauses

To correct comma splices:

• Use a period to separate one sentence into two.
• Use a semi-colon instead of a comma in order to combine two independent clauses.
• Keep the comma, but add a conjunction after the comma (for, and, nor, but, or, yet, so). 
• Use a dash to separate or join the clauses.
• Change one dependent clause into an independent clause.

When to use a comma

Example 1

Incorrect: The sun is out, we have to put on some sunscreen.

Correct: The sun is out. We have to put on some sunscreen.

Explanation: The incorrect example links two independent clauses connected by a comma. We fixed the comma splice by creating two separate sentences.

Example 2

Incorrect: I’m thinking of skipping English class, it’s really boring.

Correct: I’m thinking of skipping English class; it’s really boring.

Explanation: We are allowed to use a semicolon or period in order to separate two independent clauses, but not a comma. We corrected the error by using a semicolon.

Example 3

Incorrect: It’s Saturday night, let’s go out and party.

Correct: It’s Saturday night. Let’s go out and party.

Explanation: A comma should only be used if there is a dependent clause. If you can make two complete sentences, you don't need a comma.

MLA Owl