First choose a topic that creates the most emotion for you. Let's say it's lilac bushes in May. Now do some brainstorming. Write one list of words that describes the topic from all five senses—or from as many of the senses as you can use. For lilacs, you might write down: purple, tiny flowerets, cone-shaped, sweet, perfume, dancing, green leaves, branches bowing low. Now write another list of words that describe the emotions you feel from your topic. For lilacs, it might be: peaceful, joyful, sleepy, hopeful, happy, calm. Now think of things you can compare your topic to. What is it like? For lilacs, comparisons could be: like a fragrant magnet that draws me near or like an exotic perfume that entices and enchants me. Finally, describe one or more situations when the topic meant a lot to you. For lilacs, you might say: I picked a bouquet for my mother on Mother's Day or My friend and I rubbed our faces in the blossoms and giggled.
Now you have a lot of words, feelings, and experiences you can include in your poem. You don't have to include everything you wrote down while brainstorming. Go through and choose the ones that seem to fit well together. Do you want a rhyming poem or free verse? Free verse might be easier, but once you start writing, you may find that some rhymes occur almost naturally, and you'll want to go with those. Whether your poem rhymes or not, it will be rich in sensory detail, emotion, and memories, which are three key elements of poetry.