First of all, decide what you want this poem to be about.
Then write down a list of nouns, adjectives, verbs about this specific topic.
Then list out synonyms of these words in a separate section.
Next make a rough draft of the poem, trying to keep ten syllables in each line.
Count the syllables in each line. See if they follow the unstressed, stressed pattern. The rhyme in each line should sound like
ba-BUM / ba-BUM / ba-BUM / ba-BUM / ba-BUM
If words you have written don’t match the syllable pattern, use the list of synonyms you made to replace words.
If it doesn’t work, try rearranging the sentence structure
Read the poem aloud to make sure it has the correct meter.