Use an em dash to set off a parenthetical phrase for emphasis
Use an em dash to indicate an abrupt break in thought
Use an em dash to introduce a list or explanation
Use an em dash to replace commas, parentheses, or colons when stronger separation is needed
Use an em dash to show interrupted dialogue
Do not put spaces before or after an em dash in standard American English
Use one em dash between the surrounding words or clauses
Avoid overusing em dashes in formal writing
Keep punctuation consistent with the style guide you are following