I wrote a new one
I cant think of something after "I really like you,"
My advice is either to not write a poem and just tell her in person or tell her your poem in person.
If you do write a poem though don't stick it in her locker lol, as soon as she sees it she'll probably throw it away.
Also, don't listen to littledude's shallow "all girls only want love! if you want to do anything romantic you're a pathetic loser" attitude; it just doesn't work like that unless you find some easily convinced girl who has already done it plenty of times before.
EDIT: You've never talked to her lol? Get to know her first, say hello, help her if her books drop or something. Girls sometimes find it weird when a guy that they don't even know writes a love poem for them, even if it seems romantic, they'll still probably think it's weird.