Choose a love poem that is long enough to turn into a rap of one minute or more in length. Ideally, you will choose a free-form poem as some poetic forms, such as haiku, are bad candidates to turn into a rap song. Additionally, you can choose a poem that rhymes at the end of each line, as this rhyme scheme will easily convert into a rap.
Decide if you will rap to an accompanying musical beat. Beginners are better off rapping to a beat as it facilitates better delivery and a consistent flow. Also, a beat gives you a chance to rehearse your music and develop a sense of where you should be in your verse as you perform.
Rewrite the love poem to incorporate a rhyme scheme either with the syllables that end words or the way you emphasize sounds. Consider changing the words that end each line in the poem if it helps your rap sound maintain a consistent rhyme scheme or cadence.
Rehearse the rap. Practice the cadence and tone that will go into the rap performance. The primary difference between rap and poetry is that a poem can be read, while rap must be heard and experienced. It is also important that your body language and vocal tone reflect this difference.
Get feedback from friends and any others you know who write, perform or appreciate rap. If you receive useful advice, refine your rap to reflect it. When you feel ready, perform the rap for the target of your affection.