Take a moment to step outside or walk to a favorite park or hiking trail. If possible, find a spot further away from people. You want to be able to notice the natural sights, sounds, textures, smells, etc. around you. Is there a breeze? Does a leaf on the trail catch your eye? Pick up a rock or twig. How does it feel in your hand? Look at the space around you. What parts of it feel beautiful? What parts seem wild, untamed, maybe scary? How do you feel, being in this space? What do these things around you remind you of? Are there birds or other animals? What signs of life do you see? Are there hoof prints, paw prints, feathers, etc.? Are there signs of death? How so?
You can use these questions to help get started on a poem. If you want to look for even deeper connections, consider these questions as well. Can anything be described in a human way (personified)? Is there a tree that is shaped similar to a person? Do the wildflowers remind you of being soft and fragile, or do they seem more like a strong, determined weed? Do you know anyone who exhibits these same strengths or frailties? Does the wind or rustling of tree leaves remind you of other sounds? Maybe they sound like music or a voice.
These are just a few possibilities to consider for this exercise. Write whatever and however you feel works best for you! The point of a nature poem is existing within nature. Sit with it, take time to look at and hear everything, and try to find a connection with it.