 Use commas after an introductory word, phrase, or clause.

 Instead, Van decided to take the summer off.  The next morning, the newspaper reported the election results.  Since the class did not meet yesterday, Mitzi spent the day in the library.

 Reluctantly the instructor agreed to postpone the test. › Reluctantly, the instructor agreed to postpone the test.  During the seventh-inning stretch Harry Caray led the fans in “Take Me Out To The Ball Game.” › During the seventh-inning stretch, Harry Caray led the fans in, “Take Me Out To The Ball Game.”

 In fact the car has had very few problems. › In fact, the car has had very few problems.  Yawning loudly Eric said, “Is it morning already?” › Yawning loudly, Eric said, “Is it morning already?”

 When Kim plays video games she shuts out the world. › When Kim plays video games, she shuts out the world.  Even though English is a hard subject I still come to class. › Even though English is a hard subject, I still come to class.

With most of these sentences there is sort of a natural pause, one that would be there if the sentence were being read aloud. This pause can be after a single word, a phrase, or even a clause. At the end of any of these is where the comma goes. If the sentence can be read aloud and a pause is given, then a comma should be placed there when the sentence is written.