People who don’t know where to place a comma can figure it out pretty quickly if they will see their document as a roadway for others that requires sign posts planted in the document for the traveling reader instead of hard-to-figure-out punctuation marks.
Like a period, the question mark, and quote marks, a comma is just a sign post for a reader whose job it is to decode those words you have written. Of all the punctuation marks, the comma gives creators of workplace documents the most trouble.
You can see the use of the comma this way.
Start seeing your words on the page as directions for a traveler who is moving through your document and you will quickly realize that a comma is a corner where you make a turn. Look at your sentences, where does the idea shift? Add a comma if it is inside the sentence. Add a period at a dead end--a completed thought.
A common problem these days is the use of a comma to connect two whole sentences instead of a period. It is so common that people don’t see anything wrong with it. One day—maybe tomorrow—the comma splice (the name for this type of comma mistake) may no longer be considered wrong. Presently, however, that connection of two whole sentences is still called a comma splice and it is still considered wrong. (Note that I did not add the traditional comma before the word “and” inside that previous sentence because the comma before the conjunction has become obsolete. I agree with that shift in thought about the overuse of the comma. One really doesn’t need two old-fashioned sign posts—a conjunction and a comma-- to make a shift there.)
When you have written a complete idea, use a period to mark the conclusion of that idea—the end of the road. When you ask a question, use the question mark. When you want to show excitement, use the exclamation point but restrain yourself. Exclamation points cause the reader’s eyes to widen and to stop and take in all that excitement. Do as little as possible to slow down your reader. Any deviation from the normal pace of commas and periods can cause a slow-down or a stall. Quote marks often do that because they are often used unnecessarily. When you are quoting someone, do use the quote marks but make sure the language inside the quote marks is exactly what the speaker said. You wouldn't want someone saying you said something a certain way if you didn't, so don't do that. If you are not quoting exactly, you are summarizing or paraphrasing. If it is not an exact quote, you do not need the quote marks.
Do not use the quote marks to set off words that you consider special. Many people do that. Don’t do it. Quote marks used that way slow down your traveling reader and cause your reader to try and translate what you mean by enclosing some words in quote marks. Figure out the words you need to use there instead and use them precisely Quote marks that are meant to set off words burden the reader unnecessarily. Punctuation marks should free a reader to focus on the words and decipher their meaning.
That’s what punctuation marks really do. They don’t exist to torture you. They don’t exist as some private domain that only English teachers understand. They are sign posts for a reader who is moving quickly through your document and needs to know where to turn, stop or find out more by asking the question with you.