(and, or/nor, but, so, for, yet) that joins independent clauses (a clause or phrase strong enough to be a sentence by itself).
Jawas are a great source for droids, but the droids might be stolen.
Sand People travel in single file to hide their numbers, and they ride banthas.
After an introductory word group
The weapon of a Jedi, the lightsaber is an elegant weapon of a more civilized age.
When Jawas come to town, it is a good idea to hide your droids.
As a double major in the Dark Side of the Force and Sith History, I have learned how to manage my time carefully.
Between items in a series
The Sith believe in using strength, power, passion, and rage to overcome their enemies. Boba Fett uses a flamethrower, a carbine, and other devices to capture bounties.
Use commas to set off non-restrictive elements such as appositives, adjective clauses, or other defining and extra information.
Tauntauns, which smell worse on the inside, can be used as a sleeping bag in emergency situations. (Adjective clause)
An adjective clause is used to provide additional information and/or description within the sentence. They typically begin with which, that, whom, whose, or who.
Jabba the Hutt’s best-selling book, Changing Dancers into Rancor Toothpicks, was the result of many years of research. (Appositive)
Appositives are nouns or noun phrases that provide extra information or clarification, though they could have outright replaced the original noun. In this case, Changing Dancers into Rancor Toothpicks could have been used in the place of book.
Between coordinate adjectives not joined by and, don’t use a comma between cumulative adjectives
Coordinate adjectives: The Force is a powerful, guiding tool that can be used for good or bad.
A quick way to look for coordinate adjectives is to insert and between the adjectives. If the sentence still works and sounds right, then it is a coordinate adjective.
Cumulative adjectives: The Jawa was rolling around in his rusty scrapheap like George Lucas swims in money.
Inserting and between rusty and scrapheap would disrupt the sentence.
Use a comma to set off transitional and parenthetical expressions, absolute phrases, and contrasted elements.
Boba Fett did not understand why someone would kill a bounty if they were worth more alive; moreover, he didn’t understand why this was difficult for others to grasp. (Transitional expressions: moreover, in other words, as a matter of fact, for example, etc.)
The Force, so far as we know, can only be wielded by certain individuals. (Parenthetical expression)
Parenthetical expressions are not really part of the main idea of the sentence, or they interrupt the main sentence. Some common parenthetical expressions are: By the way, as a matter of fact, after all, and well. When spoken, parenthetical expressions are indicated by a pause before and after the expression. In writing, these pauses are indicated with commas.
Darth Vader and Grand Moff Tarkin made galactic history in 0 BBY, the Deathstar having destroyed billions of sentient beings simultaneously. (Absolute phrase: phrase that modifies the entire sentence)
A bounty hunter seeks monetary, not gratitude-based, compensation. (Contrast)
Emphasize nouns of direct address, the words yes and no, mild interjections, and interrogative tags
No, it is you who are mistaken about a great many things. –Emperor Palpatine
Jawas are so adorable, aren’t they?
However, I used to bull’s-eye womp rats back home, and they aren’t much bigger than two meters.
Accentuate direct quotations
“Tell me the location of the Rebel Base,” demanded Grand Moff Tarkin.
“That’s not true! That’s impossible,” cried Luke Skywalker.
Dates, addresses, numbers, and titles
On May 25, 1983, “Return of the Jedi” was released in theaters.
Anakin Skywalker became Darth Vader at the Senate Tower, Coruscant, when he killed Mace Windu.
If found, please return this light saber to Luke Skywalker, at 1138 Rebel Base Ave., Hidden Rebel
Base, Yavin 4. Also, please return any hands found with the light saber. Dr. Interrogation Probe, M.D., performed Princess Leia’s interrogation.
Prevent confusion
Sometimes a comma acts as a replacement for words and acts as a signifier for the reader to provide the missing words mentally.
To err is human; to get revenge, the way of the Sith.
Words that repeat in succession may require a comma for ease of reading and clarity.
The Death Star we had thought wasn’t operational, operated.
The Rebel Alliance who we expected to win, won.
Commas can also be used to prevent your reader from grouping words together in ways that may be unintentional.
Sith Lords who can, shoot force lightning whenever they feel like it.
Try reading this sentence without the comma. It doesn’t make a lot of sense, but with it the meaning becomes clear that not every Sith Lord can shoot force lightning.