In order to write a very small poem, you can begin to think of it as a word picture. Choose a small object or experience - look around your room, your house, your school, your neighbourhood - find a small thing to write about that intrigues or interests you.
Think of how to describe it with one simple image or simile or metaphor. You are aiming to show other people how you see the small thing in a new way, a view they might not have thought of. Even a gum leaf can inspire you. E.g.

Gum Leaf
a green road map
for ants.