A comma with the right coordinating conjunction can be used to join two independent clauses (the other option would be a semicolon with conjunction). In such cases, the comma comes before the conjunction, not after it. You should use the conjunction "and" instead of "but," since the two clauses are complementary rather than contrasting.

A comma should be used to separate a modifying dependent clause from an independent clause. The independent clause here is the command "make sure all the doors are locked." The dependent, introductory clause "Before you go to bed" tells when to perform the command.

A comma should be used to separate a quote ("We're so glad you made it") from narration ("she said"). Always put the comma inside the quotation marks! Also, it is correct to use a comma to separate an independent clause ("We're so glad you made it") from a dependent clause ("she said"). Again, always put the comma inside the quotation marks! Do NOT use a comma to separate verb and direct object ("made, it"). and do NOT use a comma to separate subject and verb ("she, said")

Commas should be used to separate parenthetical phrases ("in Alison's opinion") from a sentence's main clause ("The assignment was nothing more than busy work.") When you see a phrase with commas on either side, see if the sentence works without that phrase! If the commas are being used correctly, you should still have a complete sentence that makes grammatical sense.

A comma should be used to separate a dependent clause ("Studying the map carefully") from an independent clause ("the general planned his next move"). Commas should not be used to break up a subject and its verb ("the general, planned"). Never use a comma to separate a verb and its direct object ("Studying, the map")

Commas should be used to separate a dependent clause ("To finish the triathlon") from an independent clause ("you must run, bike, and swim"). Also, use a comma to separate individual verbs in sequence: in this case, "run, bike, and swim"). Do NOT use a comma to separate a helping verb from its main verb ("must, run"). The serial comma between the last two verbs ("bike, and swim") is optional, but provides clarity. Also, since all other options are incorrect, you should keep it here.

In this sentence, the correct version will use a comma to transition from a quote ("Well,") to narration ("she said,") and back to the quote ("I think I'll go for a walk."). Always put the comma inside the quotation marks! Also, in this sentence the correct version will use a comma to separate dependent clauses ("Well,") ("he said,") from one another and from the independent clause ("I think I'll go for a walk"). Again, always put the comma inside the quotation marks!

The best version of this sentence will use a comma to separate the two parts of a paired comparison. Each clause ("The more you practice" and "the easier the game becomes") should have similar syntax, or word order. This kind of sentence construction is very common in English. Try making your own similar sentences with other comparative words ("The more... the faster," "The better... the better," etc.). With practice, you'll spot the comma every time!

The correct version of this sentence will use commas to separate an appositive ("an award-winning author") from the main clause of the sentence ("Jane Doe will be signing copies of her book."). An appositive just further describes the subject, so you should have a complete sentence that makes sense if you remove it. Try reading the sentence without the phrase in commas to hear whether they are in the correct place.

A comma should be used to separate an independent clause ("The professor canceled class") from a modifying dependent clause ("which was a relief to her students"). Be careful with relative pronouns like "which." Without a comma before it, this sentence would mean that the class was a relief to her students, not the fact that their professor canceled it. Never use a comma to separate a verb from its direct object ("canceled, class")