Write several sentences on the board that don't contain commas. For example, write, "Sarah wanted to bake cookies for her mother but didn't have any eggs at home." Call several students to come to the board and put commas in their proper spots.
Read a short story out loud to the students. Give students copies of the story you're reading, so they can follow along. As you read the story, ask the students to raise their hands every time you come to a comma. When you finish the story, tell the students how they did.
Use a game of sentence scrabble to help your students practice comma placement. Give the students a worksheet with several sentences that are scrambled. Instruct them to unscramble the words to create a sentence. After they finish creating a sentence, ask them to place commas in their proper places. To give them some hints, state how many commas are needed in each sentence.
Assign worksheets during class about commas. After they're finished, ask them to trade worksheets with the student sitting next to them. Have the students grade each other's worksheets. Instruct the students to hand back the worksheet they graded, so they can see how they did.