Use onomatopoeia in poetry that's meant to be read aloud. An example is Edgar Allen Poe's poem, "The Bells," in which he describes the sounds different bells make, from tinkling sleigh bells to groaning funeral bells. By using onomatopoeia, Poe doesn't have to use more words to describe the bells' sounds.
Save words and space in comics and graphic novels by using onomatopoeia. For example, instead of a balloon with the words "He hit me!" you can simply include the word "POW!" in the drawing of someone being hit. Onomatopoeia also helps the reader imagine the sounds that go with the story.
Sing using onomatopoeia. Instead of words, make up syllables to represent the notes you're singing. Example are jazz's scat, Reggae's ska or the vocalized musical scale: do, re, mi, fa, so, la, ti and do.
Make a style choice when writing prose by using onomatopoeia instead of other methods of description. For example, you can describe how a new idea preoccupied a character or you can just say that the new idea was rattling around inside the character's head. This shows that the idea was distracting in the same way as that something rattling might distract you.