Words and Settings
In the 21st century, our vocabulary is enormous, but it was not always so. If you're writing fantasy or historical fiction, you have to be careful to make sure that the words you use existed during the time period or the approximate time period of the story.
Example: Adrenaline. It wasn't discovered until 1900, so in a story about a young man in Russian America in 1650 will not use the word "adrenaline". For an adrenaline rush, they will probably use "a rush of blood" or "rush of energy".
Another example is "firing" arrows. "Fire" as a command to use a weapon only came about after the invention of the firearm, and it took a while to spread to arrows. "Shoot" or "loose" is a better command.
There are also words that may have been there in the old days, but that had a different meaning, such as "gay". It once meant "happy", you know, so if a character in 1823 says that someone "looks gay" it means that they look happy, not that they look homosexual or stupid.
Now, I'm not saying that you have to get rid of every word that wasn't there at the time. Heck, the concept of zero is fairly recent, so a number like "30" or "105" would just be written "3 " or "1 5", and it was easy to get it confused for "3" or "15". Just keep in mind what the word is. If it's a hormone or similarly scientific word, then it probably wasn't discovered until the late 1800's or early 1900's, and if the character lives in the middle of nowhere, they wouldn't know about the word. Being careful about this will make your story seem more authentic.
This can also apply to similes and metaphors. "Fast as a striking snake" would not be appropriate in a fantasy world based off of the Canadian tundra.