Read your poem aloud and mark any phrases, sentences or words that are cliched (meaning familiar or prototypical phrasing). For example, the phrase "mad as a hornet" is a cliche that is very familiar, and therefore does not have as much impact as a more original phrasing. When you find cliches in your writing, try to think of a new and interesting way to express your ideas -- how can you create a new phrase that conveys the feeling you want to, or how can you change the cliche to make it new?
The power of many poems comes from their conciseness and compactness: poems often convey a narrative or emotion using fewer words. Try to cut down any unnecessary language that doesn't add to the meaning of the poem or the beauty of the sound. In particular, try to avoid excessive adjectives or adverbs (words that modify nouns or verbs).
Review your verbs carefully to make sure that they are active and interesting. For example, the phrase "The ball was thrown" is passive, while "I threw the ball" is active. But you could go even beyond that and use more graphic verbs. How about "I lanced the ball" or "I pelted the ball" instead of "I threw"? Look for more interesting and specific verb choices in your poems.
Watch for overuse of abstract language. Abstract language refers to words that do not have a specific, concrete meaning. Words like "love," "soul" or "happy" are vague and could mean something different to every reader. While it's fine to use these phrases sparingly and in interesting ways, avoid using them when more concrete language could be useful. For example, instead of "I feel happy when you are near," you could say "I feel sparks in my chest when you touch my hand." Using a concrete image can make your writing more vital and interesting. Aim for words and phrases that convey your meanings through the five senses.