Brevity: n. the quality of expressing much in few words.
When I was in tenth grade, I took my first literature course. It was a six week exploration of poetry. The first poem my teacher showed us was Ezra Pound's In a Station of the Metro:
The apparition of faces in the crowd;
Petals on a wet, black bough.
I, in all of my 16-year-old knowledge of the intricacies of what poetry is, informed my teacher that those two lines were not a poem.
"You don't think so?"
"No. They don't rhyme, they are just one metaphor, and did I mention they're only two lines?"
She sure showed me.
Importance in Poetry
Pound's poem is considered such a great work because he inserts several layers into a single image. Using only 13 words he evokes an entire painting within the reader's mind. You can hear the sounds of the trains, see the fatigue of a mother wrestling with her cranky toddler, watch the homeless man leaning against a pillar swaddled in blankets scratching his dog behind the ears. In just 13 words, Pound has put you in the middle of that train station, and then let you wander around to observe what you will.
Great poems rely on the imagination and intelligence of the reader. It is a conversation, not a lecture. Poems that stick with us provide enough information to leave an impression, to define an idea. The writer expects that the reader will have their own interpretations of an image. Brevity in poetry helps a writer focus the reader's attention on a specific thought path, so that eventually they draw similar conclusions.
So How Does It Work?
"Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away." -Antoine de Saint-Exupery
That is the essense of it. Your first drafts will likely be long, meandering idea dumps. And that is perfectly fine. When inspiration hits, go with it. Let the words flow out of you however you like them to flow. It is in the editing phase that brevity becomes important, because it is in that stage that you ought to start thinking about your audience, the message you wish to convey, and the tools you want to use to convey it.
Avoid generalizations. Using words that can be applied to several different ideas (e.g. "something", "anyone", "all the time") is generally not a good idea. Those types of phrases don't give your reader a direction to follow, and your message can get lost in personal interpretation.
Cut out unnecessary words. The usual culprits are articles and prepositions. These tiny words can make your writing much more verbose than it needs to be. When I edit, I highlight every article and preposition, then cross out the ones that can be crossed out without losing clarity.
Watch out for cliches. I am not one of those writers who avoids a cliche at all costs. Cliches are alright in some instances, but they should be used with caution and intelligence. When you find one, try to find a way to phrase your thought that reflects how you feel about/interpret the subject.
Ask yourself if the reader needs this information. A lot of times, writers insert much more information in a poem than is actually needed to convey their message. If your words aren't conveying something important, they're wasting space. A good critic can help you find these words and phrases and put them back in their box.
Read. A lot. You don't learn how to write without reading. So read everything, and analyze how other writers manage to package their ideas into as few words as possible. I also recommend following good critics here on dA and reading their critiques. (I'm thinking specifically of thorns, ShadowedAcolyte and Nichrysalis here.) Often the problems you're having in writing, many other writers are also having. Reading critiques is a great way to pick up tips for improvement without having to get critique on your own work.
A Few Examples from DeviantART
Here are just a few pieces from my favorites gallery that exemplify how brevity works in poetry. Have a read, and suggest some of your own favorites in the comments below!
open opinionthe empty mouth of poetry
all blackened throat
and stunted teeth
all these walls
all these walls
You just need focus,
the tree is the simpler task.
One must expect blurred edges,
truth inferred rather than seen.
I was Eros once.I stuffed my throat,
and pockets full of roses.
I tied myself up with heartstrings.
I set myself on fire.
The Wilful EmptyIt's that spot on the wall.
Where wolfish shadows play,
Uncoffined eyes dancing
On their leash, hooked
To that spot on the wall.
Swept empty by soft fingered
Brooms, gaunt ribs tonguing
Their cage, white fowls pecking
At that spot on the wall.
The most important crime
Must be repeated, eyelashes
Knocking at the door; the most
It's that spot on the wall.
BreakingOne day, you will open the cupboard
to find a wine glass or some Tupperware
and the world will, without warning
or alarm, roll off the edge of the shelf
and coming crashing down.
The oceans will splash onto the linoleum,
onto the rug. All the dust in all the deserts
will rain down onto the couch and coffee table,
the hills will crumble, the mountains will break,
all the windows in all the cities will shatter
and fall, a thousand dangerous miles of glass
glittering on your kitchen floor.
Everything will hush.
Exhale the breath you are holding,
and go look for a dust pan, for a broom.
Remember, brevity doesn't always mean writing a very short poem. It is being economical and conscious about your word-choice. Practice makes perfect, so go forth and write!