Write a sentence of four or five words. Try not to anticipate the sentence as you write it. Write down a random word, then feel for the next one, letting it suggest itself equally from sound and sense. This is your first line.
Make a stanza of four lines, each line built from a series of words using the same first letters as the first line. So if “Frank took everything seriously” is line 1, then lines 2 and 3 are formed F___ t___ e___ s___. Let line 4 repeat line 1 exactly.
Feed forward, borrowing a word from somewhere in the first stanza to start a second stanza.
Follow the same rules going forward, except when you don’t.
Play the lines, so that the rule following, rule shifting, and rule breaking all feel like gestures, like compositional moves.
Continue for four or five stanzas.
Break all the rules — or double down on them extravagantly — for the last line.
This is a warmup to get your vocabulary moving, but do pay attention if any images that surfaced through the constraint surprise or interest you.