A New Rule for Commas

1. Just as you use a comma to separate a dependent clause that appears at the beginning of a sentence from an independent clause which follows, you often use commas to separate introductory phrases (those over four words) from a following independent clause. For example, look at these sentences I borrowed from the OWL website:

Having finished the test, he left the room.
To get a seat, you'd better come early.
After the test but before lunch, I went jogging.
The sun radiating intense heat, we sought shelter in the cafe.

In a like manner, places a comma after some common introductory words, like yes, however, well. For example, see the following sentences, again borrowed from the OWL website:

Well, perhaps he meant no harm.
Yes, the package should arrive tomorrow morning.
However, you may not be satisfied with the results.

Here is a link to website where I found the examples above:

http://owl.english.purdue.edu/handouts/grammar/g_comma.html