“Questioning a comma, he will shake his head and say in his soft voice that he realizes perfectly well what a lot of time and thought have gone into the comma and that in the ordinary course of events he would be the first to say that the comma was precisely the form of punctuation that he would have been most happy to encounter at that very place in the sentence, but isn’t there the possibility — oh, only the remotest one, to be sure, and yet perhaps worth considering for a moment in the light of the care already bestowed on the construction — that the sentence could be made to read infinitesimally more clearly if, say, instead of a comma a semicolon were to be inserted at just that point?”
— Brendan Gill, on editor William Shawn —
“Here at the New Yorker,” Random House 75

COMMA

A mark of punctuation used to indicate a division in a sentence, as in setting off a word, phrase, or clause, to separate items in a list, to mark off thousands in numerals, to separate types or levels of information in bibliographic and other data.

Consider the lowly comma.
If you regard it as a mere flyspeck with a tail, that may account for the some capricious uses (and non-uses) of it that appear from time to time.
Example 1: “The luncheon was in honor of three new council representatives from Australia, Cuba, and Yugoslavia. . .”
Without a comma after “representatives” the meaning is that three new representatives are replacing three old ones.
A comma (perhaps preferably a dash) would have brought out the correct meaning, that representatives of the three countries were new to the council.
Example 2: “. . . as the lips and skin of the mask are in natural colors, the inventor says, a very lifelike illusion is created.”
Insert a comma after “says” to set off a parenthetical phrase.

— Paul B. Snider
Professor of Journalism
Bradley University
Peoria, IL

Put commas within closing quotation marks.

“I may forget your name, but I always remember a face,” he said.
“John talks a good game,” says Steve, “but when it comes to taking action, Robert is much better.”

— Owl On-Line Writing Lab —

Use commas to separate elements in a series, and DO
put a comma before the conjunction in a simple series
of three or more items.

The flag is red, white, and blue.
He would nominate Tom, Dick, or Harry.

— The Elements of Style —

Using commas with the word “however”

Using “however” to begin a sentence:
If “however” is used to begin a sentence, it must be followed by a comma, and what appears after the comma must be a complete sentence.
However, there was no need to repeat the data entry.

Using “however” as an aside:
“However” can be used to interrupt a sentence. Use a comma before and a comma after “however” when you use it in this way.
It is, however, extremely difficult to identify all the relevant variables.

— University of New England —