Choose an animal you would like to describe. Pick an animal that has physical and behavioral qualities you find interesting. For instance, a cheetah, spotted and fast, is a captivating mammal. Or, choose a number of animals to begin with and then whittle the animal list down to one.
Start with a physical description. Jot down a few physical characteristics about the animal, such as its fur, skin, eyes, tail, neck, teeth or ears. For example, if your animal is the elephant, note the gray leathery skin, the soft eyelashes above dark eyes, the hair-tipped tail, circular feet and large floppy ears.
Add observations of the animal. If you are lucky enough to get to see the animal in action at a zoo or if you have the animal as a pet, make observations about how the animal moves, sleeps, eats, communicates and interacts with other animals and you. If you observe a rabbit, notice how it leaps and stands on its haunches, sleeps in a ball, munches tufts of grass, squeaks to communicate with other rabbits and bunnies and wiggles its nose when you pet it.
Start with an image. Every first line in a poem produces some sort of picture in the reader's mind. For example, you may begin the poem very simply by writing "The alligator floating in the muddy water intrigues me." You can later revise this, or keep it as it is.
Mix in descriptions and actions. Make sure to fill your poem with verbs as well as adjectives. Imagine the exact images you see when you think of the animal, or how you recently saw the animal. Let the first images you see, and the impressions you have, guide your writing. Use the physical, behavioral and observational notes to punctuate the images in your poem.