Pay constant attention to punctuation in everything you write.
IV.

Punctuate your sentence while you are writing it.
V.Understand what you are printing.

_This is of supreme importance._ Punctuation is an aid to understanding.

You cannot correctly punctuate anything that you do not understand.
THE COMMA The comma is by far the most difficult of all the punctuation marks to use correctly.

Usage varies greatly from time to time and among equally good writers and printers at the same time.