Writers often compare one thing to something else, to help the reader see the object or person in a new light. Similes are figurative devices that compare things using the words "like" or "as." For example, "she shines like the sun," is a simile. A metaphor also compares two things, but doesn't use "like" or "as." "That pig cheated on her" is an example of a metaphor.
Personification gives non-humans human-like qualities. For example, "the flag danced in the wind" and "traffic was crawling" are examples of personification. Personification also involves using pronouns to refer to objects. For example, calling a boat "she" is personification.
Hyperbole involves exaggerating to make a point. One example of hyperbole is saying, "I told you a million times not to do that."
Onomatopeia refers to words that sound like the thing they are describing. For example, the word "zip" sounds like the sound a zipper makes, and the word "drip" sounds like water dripping.
An idiom is a common phrase, and is often a cliche. Two idioms in American English are "made of money" and "off the record."
Synecdoches use a part of something to refer to the whole. For example, when you ask someone to "lend you a hand," you are actually referring to the entire person---you don't really just want his hand.
A pun is a play on words. A writer can use similar-sounding words to convey two meanings. Puns usually aim to be humorous.