(1) the first line and the last line must be the same
(2) the first word in each line, when read downwards, must be the same as the first and last lines
(3) the last word in each line, when read downwards, must be the same as the first and last lines
(4) punctuation can be altered, and homonyms and homophones are allowed
It is very hard to get a half way decent poem out of this, but that doesn't mean you can't try. Here is my model example:
Square Poem
I am a square poem. I
am boring and nerdy. I am
a complete nonentity – a
square box of air. A square
poem? Is that even a poem?
I am a square poem. Aye!
Get writing!