Record a passage you've written by reading it aloud. Then listen to it and analyze it. If it sounds stiff or false to the ear, it will probably seem that way to a potential reader. If you come up with new ideas after listening to the recording, write them down.
Recite paragraphs and phrases from your favorite authors and poets. Take note of what you like about the vocabulary, sentence structure and overall voice. Use what you like in your own writing. Don't imitate the style outright, but turn it into your own voice.
Give readings at your local café or bookstore. The audience reactions will let you know what passages work and which don't. If your story or poem translates well as a spoken word piece, it will be just as powerful in written format.
Correct any sentences or sections that contain too much alliteration or stilted language. The sentences need to flow together in prose as well as poetry.
Read passages from new work aloud every so often. Writing is entertainment first, and by listening to the words and also reading them on the computer screen or paper, you will get a better idea of what will work for the audience. Listen for the musical flow and continuity of the words.