First, start memorizing as soon as you can. If you have four days, for example, try breaking the poem up into four equal sections. Be sure not to start at the first of the poem each time you do it. In fact, I know one student who memorizes the last stanzas first; that way, the closer she gets to the end, the surer she is of her material because she has said it more often than she has said the first part. You will have to set aside some time for this project. One way might be to write the stanzas of the day out on paper then carry the list with you. Take a long walk alone and learn each stanza as you walk along. That way you can recite the lines, and no one will bother you (unless you live in the city, and even then, you might fit in just fine!). If you have a tape recorder, record the lines and check your memory that way; otherwise, work until you can write down each stanza perfectly.
Pay attention to the rhyme of the poem because many times the end rhymes will help you remember the next lines. Once a poem is memorized, it is yours to treasure forever.