Uses of the Comma

A comma is a versatile punctuation mark, serving ten basic functions. Here’s an enumeration, with examples.
1. Separate the elements in a series: “Groucho, Harpo, and Chico developed the philosophy called Marxism.”
Many periodicals and websites, and most colloquially written books, omit the serial, or final, comma, but it is all but mandatory in formal writing and is recommended in all usage. As language maven Bryan Garner observes, “Omitting the serial comma may cause ambiguities, whereas including it never will.”
2. Separate coordinated independent clauses: “I like the Marx Brothers, but she thinks they’re too silly.” (An independent clause is one that can stand on its own as a sentence but is linked with another by a conjunction and/or a punctuation mark.)
Exceptions include sentences with closely linked clauses (“Go to the window and see who’s there”) and those with a compound predicate (“The Marx Brothers are known for their puns and their sight gags”).
3. Separate an introductory word (“Naturally, I agree with you”), phrase (“Last summer, I went on a long vacation”), or subordinate clause (“If you’re too busy now, wait until later”) from the remainder of the sentence.
4. Separate an optional parenthetical element from the remainder of the sentence. “We have, in a manner of speaking, won despite our loss.” (The phrase “in a manner of speaking” could also be set off by em dashes or parentheses, depending on whether the writer wishes to emphasize the interruption of the statement “We have won despite our loss” or wants to diminish it as an aside.)
5. Separate coordinate adjectives from each other: “I could really use a tall, cool drink right now.” (Do not separate non-coordinate adjectives with a comma; https://www.dailywritingtips.com/coordinate-and-noncoordinate-adjectives/ explains the difference between these two types of adjectives.)
6. Separate an attribution from a direct quotation: “She said, ‘Neither choice is very appealing’”; “‘That’s not my problem,’ he replied.” (A colon may be precede a formal pronouncement or an attribution that forms a complete thought, as in, “He had this to say: ‘Her point is irrelevant.” Omit punctuation when the attribution is implied, as in “Your response ‘Her point is irrelevant’ is evasive.”)
7. Separate a participial phrase or one lacking a verb from the remainder of the sentence: “Having said that, I still have my doubts”; “The deed done, we retreated to our hideout.”
8. Separate a salutation from a letter (“Dear friends,”) or a complimentary close from a signature in a letter (“Sincerely,”). A colon should be used in place of a comma in a formal salutation.
9. Separate elements when setting off a term for a larger geopolitical entity from that for a smaller one located within it (“Santa Barbara, California, is located on the coast”) and for elements of street addresses (“1600 Pennsylvania Avenue, Washington, DC”) (and dates (“January 1, 2013”).
10. Separate groups of three digits in numbers: (Let me tell you how to make your first 100,000,000 dollars.” (Because large numbers are difficult to scan, it’s usually better to use one of the following forms: “100 million dollars,” “one hundred million dollars.”)

From

Daily Writing Tips

Watch out for the following deadly usages.

from Daily Writing Tips:
Tried-and-true words and phrases are convenient, but they are also truly trying -- as with clichés, when a writer relies too heavily on stock usage, the resulting prose is tired and uninspired. Watch out for the following deadly usages.
1. After having: “After looking around, I chose a seat” is fine, and so is “Having looked around, I chose a seat,” but “After having looked around, I chose a seat” is redundant. “Having” means that the action has already been performed, so the context is clear that the writer is writing after the fact.
2. Aged: Identifying the age or age range of a person or a group with this word puts the subject(s) in a category with cheese or wine. Write “50 years old,” for example, instead of “aged 50 years,” or “ages 21–34” rather than “aged 21–34.”
3. Aggravate: To aggravate is to make something worse, not to bother, annoy, or irritate.
4. And also: And and also are redundant; use one or the other.
5. Anticipate: To anticipate is to foresee (and perhaps act on that foresight), not to expect.
6. Anxious: To be anxious is to feel distressed or worried, not eager.
7. Approximately: How about using about instead? Save three syllables. For scientific or technical references, approximately is fine, but it’s a bit much in most other contexts.
8. As to whether: “As to” is extraneous; use whether only.
9. At this point in time: Omit this meaningless filler.
10. Basically, essentially, totally: Basically, these words are essentially nonessential, and you can totally dispense with them.
11. Being as/being that: Replace these phrases with because.
12. Considered to be: “To be” is extraneous; write considered only, or consider deleting it as well.
13. Could care less: No, you couldn’t. You want to convey that it’s not possible for you to care
less, so you couldn’t care less.
14. Due to the fact that: Replace this phrase with because.
15. Each and every: Write “Each item is unique,” or “Every item is unique,” but not “Each and every item is unique.”
16. Equally as: As is superfluous; write equally only.
17. Was a factor, is a factor, will be a factor: If your writing includes one of these phrases, its presence is a sign that you’re not done revising yet; rewrite “The vehicle’s condition is a factor in performance,” for example, to “The vehicle’s condition affects its performance.”
18. Had ought: Had is redundant; use ought only.
19. Have got: Got is suitable for informal writing only; if you’re referring to necessity, consider must rather than “have got,” and if the reference is to simple possession, delete got from the phrase “have got.”
20. In many cases/it has often been the case: Reduce the word count in statements containing these verbose phrases by replacing “in many cases” with often, for example.
21. In the process of: This extraneous phrasing is acceptable in extemporaneous speaking but unnecessarily verbose in prepared oration and in writing.
22. Is a . . . which/who: If you find yourself writing a phrase like this, step back and determine how to write it more succinctly; “Smith is a man who knows how to haggle,” for example, can be abbreviated to “Smith knows how to haggle.”
23. Kind of/sort of: In formal writing, if you must qualify a statement, use a more stately qualifier such as rather, slightly, or somewhat.
24. Lots/lots of: In formal writing, employ many or much in place of one of these colloquialisms.
25. Of a . . . character: If you use character as a synonym for quality, make the reference concise. “The wine has a musty character” is better rendered “The wine tasted musty, and “He was a man with a refined character” can be revised to the more concise statement “The man was refined,” but better yet, describe how the man is refined.
26. Of a . . . nature: Just as with character, when you use nature as a synonym for quality, pare the phrasing down: Reduce “She had a philosophical nature,” for example, to “She was philosophical.”
27. Oftentimes: An outdated, unnecessary complication of often.
28. On account of: Replace this awkward phrase with because.
29. Renown: Renown is the noun (as well as a rarely used verb); renowned is the adjective. Avoid the like of “the renown statesman.”
30. Thankfully: In formal usage, this word is not considered a synonym for fortunately.