Use commas after introductory (a) clauses, (b) phrases, or (c) words that come
before the main clause.
Examples:
When I get hungry for Mexican food (,) I head for Taco Bell!
Because her Powerbook was broken (,) she needed to rely upon
the computers in the school lab.
Use commas to set off an adverb clause that
precedes its main clause. Adverb clauses are begun by subordinate conjunctions
such as after, although, as, because, if, since, when, and while.
Example:
While I was eating (,) the cat scratched at the door.
Note:
Do not use a comma when the adverb clause comes after
the main clause:
Example:
The cat scratched the door while I was eating.
Examples:
Participial Phrase:
Having finished the test (,) she left the room.
Infinitive
Phrase:
To get a seat (,) you had better come early.
Succession of Prepositional Phrases:
After the test but before lunch (,) I went jogging.