Add a comma after the conjunctive adverbs "therefore", "consequently", "as a result", "thus", etc. at the start of a sentence to indicate that it modifies not only a word but a complete sentence or clause.

At the start of a sentence or an independent clause, "indeed", "in fact", or "as a matter of fact" should be preceded by a semicolon or a period as well as followed by a comma.

In general, add commas to set off words and expressions that interrupt the sentence flow (however, on the other hand, by the way, etc.)

At the start of a sentence, add a comma after the phrase "on the contrary" or to the contrary. In mid-sentence, use a comma before and after "on the contrary" to state that a previous idea is incorrect.

As an introductory phrase, use a comma after "in contrast" or "by contrast" to show a clear difference between two o more things.

Use commas to set off parenthetic expressions and nonessential words, phrases, or clauses. Do not use commas to separate essential or restrictive information.

Generally, we should add a comma after an introductory phrase. The comma, however, may not be necessary if the introductory phrase begins with a preposition, or it is very clear and brief (no more than three or four words).

Do not join two complete sentences with a comma (also called comma splice). You can fix it by adding a semicolon, placing a period, or using a conjunction.

If each element of a numbered or bulleted list is a complete sentence, capitalize the first word and place a period at the end. If the elements of the list are single words or phrases, capitalization and punctuation marks (including commas) are optional.