Punctuation is invisible to a reader, up until it strays from the standards of the English language. At best, poor punctuation will confuse your readers; at worst, it will annoy and frustrate them.
In the same way that you need to know traffic rules to successfully drive a car, or you need to understand music notation to be a successful composer, you need to understand punctuation to be a successful writer—no matter what your definition of success is!
Overuse of exclamation points and question marks
One mark per sentence is enough, and exclamation points should be saved for when they are truly necessary.
Don’t: “You lost the launch codes?!!?! We’ve got to nuke them first!!!”
Do: “You lost the launch codes? We’ve got to nuke them first.”
Comma splices (run-on sentences)
When you have two complete sentences that can stand on their own, they must be joined in one of three ways: a coordinating conjunction and a comma, a new sentence, or a semicolon.
Don’t: “My dog is viscous, he ate the mailman.”
Do: “My dog is viscous, and he ate the mailman.”
Do: “My dog is viscous. He ate the mailman.”
Do: “My dog is viscous; he ate the mailman.”
Too many commas, or not enough
Use commas only when needed to make the meaning clear. Comma use is a broad topic, but in general use commas for the following purposes: to separate items in a list, to join a dependent clause to an independent clause, and to separate absolute phrases.
Don’t: “I put on my black, wool, ski mask and, walked into the bank.”
Do: “I put on my black wool ski mask and walked into the bank.”
Don’t: “Well I don’t believe you.”
Do: “Well, I don’t believe you.”
Don’t: “I robbed the bank with a gun a knife and a T-shirt cannon.”
Do: “I robbed the bank with a gun, a knife, and a T-shirt cannon.”
English has standard methods for punctuating dialogue. If you have a speaker tag (“he said”) then you need to end the dialogue line with a comma. If you don’t have a speaker tag, then use a period.
In nearly all of the world, dialogue is set off with double quotes “like so” and not with single quotes.
Don’t: “Put down the rocket launcher.” He said.
Do: “Put down the rocket launcher,” he said.
Don’t: “You put yours down first!” She replied.
Do: “You put yours down first!” she replied.
Don’t: “It’s your turn to do the dishes.” He muttered. “And I’ll see that you do.”
Do: “It’s your turn to do the dishes,” he muttered, “and I’ll see that you do.”
Don’t: “Never in a million years,” she pulled the trigger.
Do: “Never in a million years.” She pulled the trigger.
Colons versus semicolons
You almost never have to use a colon or semicolon—the sentences can usually be rewritten to avoid them if need be. In general, writing is often stronger and easier to read if it’s broken up in separate sentences instead of joined with colons and semicolons.
Use semicolons to link together related ideas.
Join two related sentences (independent clauses):
Don’t: Clifford bent down the branch, he wanted to launch the trapped cat.
Do: Clifford bent down the branch; he wanted to launch the trapped cat.
Connect list items that contain commas to avoid confusion:
Don’t: Watch out for hazards, namely, potholes, children, pets, and animals, zombies and ghosts, and angry police officers.
Do: Watch out for hazards: potholes; children, pets, and animals; zombies and ghosts; and angry police officers.
Use colons only after a complete sentence to define an example or a list.
Don’t: I dislike: dogs, frogs, logs, and bogs.
Do: The things I dislike all rhyme: dogs, frogs, logs, and bogs.
Do: I dislike dogs, frogs, logs, and bogs.
Hyphens versus dashes
Fiction writing typically uses three sizes of dashes and they all do different things:
Hyphen (-) is used for certain compound words. When in doubt, use a dictionary to look up the compound word to see if it is hyphenated. More details here.
Don’t: I am twenty one years old today, and my stupid ass friends are coming over to party
Do: I am twenty-one years old today, and my stupid-ass friends are coming over to party.
En-dash (–) is wider than a hyphen (the width of the letter N) and is used in specific situations: separating numbers, and showing opposing sides. You can make an En-dash with Alt+0150 on your keyboard (Option+0150 on a Mac). More details here.
Don’t: The score of the Brazil-Germany soccer game was 7-1.
Do: The score of the Brazil–Germany soccer game was 7–1.
Em-dash (—) is very wide (the width of the letter M) and is one of the most versatile punctuation marks. You can make an Em-dash with Alt+0151 on your keyboard (Option+0151 on a Mac). More details here.
Em-dash in place of a colon
Option 1: My family only eats one thing: stale beans.
Option 2: My family only eats one thing—stale beans.
Em-dash in place of parentheses for emphasis
Option 1: Ronald lit a cigarette (the one I had poisoned) and took a deep drag.
Option 2: Ronald lit a cigarette—the one I had poisoned—and took a deep drag.
Em-dash in place of commas for emphasis
Option 1: I returned to the scene of the crime, ten years later, and ate a burger.
Option 2: I returned to the scene of the crime—ten years later—and ate a burger.
Em-dash in place of an ellipsis for more convincing dialogue
He got down on his knees. “But honey, I’m sorry, I…”
She glowered. “Shut your face!”
He got down on his knees. “But honey, I’m sorry, I—”
She glowered. “Shut your face!”
Note how the use of the em-dash changes the effect of each sentence. Also, while em-dashes are fun, make sure not to over-do it. Use them sparingly!