Choose a poem that you like. You'll be more likely to read well if the subject matter is something that moves you. Make sure the length of poem is suitable for you as well. Some people may have no problem reading a ten page saga, while others may prefer something much shorter.
Give yourself plenty of time to review the poem before you have to read it to others. Practice reading the poem out loud until you're familiar with its structure and flow. Determine how to pronounce any new or difficult words.
Make a copy of the poem and use a pencil to mark problem areas. Identify where you should pause, which words to emphasize and any other information that may be useful as you read. The visual cues will help you stick to your reading plan once you get in front of the audience.
Slow down. Many people speak quickly under normal circumstances; once they get in front of a crowd they may become nervous and their speech becomes even faster and mumbled. Listeners will be able to understand you more easily if you slow down and enunciate.
Keep the tone of your voice normal. You don't need to get overly dramatic.