This idea for writing a poem comes from John Drury, author of Creating Poetry.

Make a list of alliterating words, grouping them in threes. (Go through the alphabet to trigger ideas.)  Words can be nouns, verbs, or adjectives: bridle, breathe, brimming.  Notice that the alliterating sound can be a combination (such as “br”), as well as a single letter.  When you have a list of about ten trios, begin a poem that uses them sparingly (maybe in a group every four lines).  Don’t feel you have to use all the groups, and don’t go in alphabetical order.  Jump around, fiddle with the words (“breath” becomes “breathless” or “breed” or “beard”).  Let the words you’ve listed lead you to the poem you write.