Choose a poem as a source of inspiration. The original work may be a classic or a contemporary piece, but well known poetry works best. Ideally, you should have parts of the original committed to memory.
Study the style and tone of the original. Make note of its rhyme scheme, which is the pattern of rhyme within the work. For instance, do every two lines rhyme with each other, does every other line rhyme or do words within the same line rhyme? Also, pay attention to the meter -- how the work uses stressed and unstressed syllables -- within the original. Your parody will mimic these elements.
Choose a subject for your parody that differs greatly from the original. The greater the difference in subject, the better. For example, consider Weird Al transforming singer Madonna's song "Like a Virgin" into "Like a Surgeon." By choosing a fresh topic for his song parody, Weird Al adds humor while keeping the tone playful, rather than critical.
Draft your parody, incorporating your new subject while using the meter, rhyme, rhythm and language of the original.
Read your parody poem aloud. Ask yourself whether it follows the flow and rhythm of the original, whether its tone is playful and whether it makes you chuckle. If it does not, make note of where your parody strays and revise as necessary.
Set your poem aside for a few days, then revisit it with fresh eyes. Again, ask yourself whether it conjures up the original poem in a playful, humorous way. If not, revise again.