Commas after transition words

Front

Correct sentence: First, grab your toothbrush.

Back

Front

Which sentence is correct?

Back

Next, grab your toothpaste.

Front

Correct sentence:

Back

Then, put the toothpaste on the toothbrush.

Front

Correct sentence:

Back

After that, wet the bristles.

Front

Correct sentence: Later, clean the sink.

Back

Later, clean the sink.

Front

Correct sentence: Finally, brush your teeth.

Back

Finally, brush your teeth.