Choose a topic. According to Middle English translator Charles Moorman, alliterative verse tended to be pessimistic and stern, with pagan undertones, formulaic word choices and a heightened awareness of social issues.
Decide on a rhyme scheme. Although alliterative verse does not require rhyme, some Middle English alliterative poems use very strict rhyme schemes. "Pearl" and "Sir Gawain and the Green Knight" combine rhyme and alliterative verse.
Plan the meter. The meter, or rhythm, of alliterative verse was important but varied greatly depending on the time and place in which the poem was written. Some poems, like "Pearl," simply alternate stressed and unstressed syllables with a fixed number of syllables per line. Old English poems divided each line in half, and each half contained two stressed, alliterated syllables in addition to multiple unstressed syllables.
Build each line around stressed syllables beginning with the same sound. Although variation exists, generally there are at least three stressed, alliterated syllables that occur throughout the line.
Adjust the line as necessary to accommodate meter, repetition and rhyme, if you have chosen to use any of these devices.
Keep the poem moving forward. While writing in alliterative verse is difficult at first, the alliteration and other devices should serve the purpose of the poem, not the other way around.
Focus first on readability and meaning. Does the poem say what you want it to say? Will your readers understand what it is saying, or did your close adherence to alliteration and other devices inhibit the meaning? Remember that even the Beowulf poet and the Gawain poet made occasional "mistakes" in terms of meter and alliteration.
Tighten the alliteration and other devices. Use a thesaurus to brainstorm other words that convey the same meaning but fit better in terms of alliteration, meter and rhyme.
Read your poem aloud. Alliterative verse was spoken aloud and needed to sound pleasing to the ear.