Read as much poetry as you can to familiarize yourself with how the craft has developed over time. This will provide with you a solid background for your own poetry, and allow you to become accustomed to various forms and styles that are used in different contexts. For example, the sonnet form is popular for expressing love, the haiku for the facets of existence, the limerick for humour, the Epithalamium for your sister's wedding, and so on.
Choose a form that best suits your intentions. Forms of poetry have different rules concerning their construction. Rhyme scheme and metric construction are important distinguishing factors, while poetic tools like end-stopping, enjambment and caesura will help you create and distill beautiful images from the sounds of your words and the form of your poem. This step is akin to finding which musical instrument you would use to play the music you are imagining.
Make lists of the words that you want to include in your poem that describe your intentions best. Samuel Taylor Coleridge, a great English poet and philosopher, once said: "Prose, words in their best order. Poetry, the best words in the best order." When writing the most beautiful poem you can, research the words that will fit together well. These words are the musical notes of your poem.
Begin to experiment by fitting your chosen words into the form you have selected. This will likely take many rewrites until you find a pleasing resonance that respects both the syllabic musicality of each word and the form of your poem. Don't be discouraged --- the result can be truly touching, like a musical phrase that stays with you for your whole life.
Break the form. Many beautiful poems are indeed very structured and trundle along obeying the rules of their metric construction. Emphatic smashing of the regular form can enhance the message of your poem, especially if you are intending a violent action of love or war, or a satirical twist or comment on poetic forms themselves. As with music, learn to play the greats, then let them inspire you to make your own.
Present the poem. Once you have written your poem and you are satisfied that it is as beautiful as you can possibly make it, present it as carefully as it deserves to be presented. Use a quality pen, such as a calligraphy pen, to finally render your art on a piece of quality paper.