Write a list of things you like about your girlfriend. Writing a poem is much easier if you know what words or ideas you want to incorporate. Think about your girlfriend and the things that set her apart from other girls.
Master the art of rhyme. Your girlfriend will know how much effort you put into the poem based on the quality of the rhymes therein. You do not have to be a critically acclaimed wordsmith to make something rhyme. Stick to words that are easy to rhyme, like heart, love, swoon or eyes. Do not try to get too advanced or you will tie yourself up in contradictions or phrases that do not make sense.
Read each line aloud after you write it. This will give you a better idea of the meter in your poem. If a poem is more lyrical, it will sound lovelier to the reader. Poems that are choppy and poorly structured will just look hasty and boring. Study up on the standard classics of poetry meter such as iambic pentameter or iambic tetrameter, both of which are often used in love poetry from masters such as William Shakespeare and Emily Dickenson.
Go for length. This does not mean you have to write an epic like Chaucer's "Canterbury Tales," but making it longer than a limerick is a must. Go for at least 10 lines. This is the average length of a poem, but remember, more is often better with love poetry.
Present the poem in a romantic fashion. Simply giving her the poem on a sheet of loose-leaf paper shows a general lack of concern. Write it on a meaningful card or a piece of parchment, which you can find at any crafts store. You could even paint the poem in an artistic way on a piece of canvas.