Well, if it's something u believe in when you're reading it out, just feel the words you are saying and say them like (if you wrote) its something you believe in and live by
My advice: When you choose your poem, PRACTICE PRACTICE PRACTICE reciting it. Recite it to yourself, in front of the mirror, to your neighbor's dog (etc) until you can (literally) quote it in your sleep. When you have to recite it for your school, why not ask a friend to sit in the audience so you can 'recite' to them? Helps avoid stage fright.
Have you chosen a poem? Why not try one from William Blake's Songs of Innocence? Here's one that probably everyone will like, called "Spring" - I'll embed it as an image at the end of this answer. It's also on fanart if the reproduction isn't good enough for you to read from here.
