Count first, decide second
Count the words in the draft. Not the lines — the words. Write the number at the top of the page. Multiply by 0.2 and round down; that is your quota. A 200-word draft has to lose 40 words and there is no negotiating.
Cutting to a quota rather than to taste is the whole exercise. Deciding line by line whether something is good enough is how a draft keeps everything; deciding that the poem is allowed exactly 160 words forces the choice.
What gets cut, in order
First, adverbs attached to verbs that already contain the meaning: walked slowly, whispered quietly, very, really, quite. Second, adjectives doing no work: small, big, nice, beautiful, sad. Third, filler openings — I think that, it seems to me, there is a kind of. Fourth, the second half of any two-clause line where the first half already made the point.
Do not cut any concrete noun, any number, any proper name, or any physical verb. Those are the four kinds of word that carry information, and a cut that removes one of them is not editing, it is amputation.
The worked example, before and after
The draft version ran to about 100 words and contained, among other things: the letter arrived on a Thursday morning as I was leaving, and I ended up reading it standing up in the hallway, and it informed me that the building had been sold and that the lease would not be renewed this year. Cutting to 80 words removed the hallway, the morning, the ending-phrase this year, and three connective clauses.
What the cut exposed is the real event of the poem, which is not the letter but the twelve-day gap and what happens to the sugar. The padding was not decoration; it was a way of postponing the sugar.
Where to stop
Run the same operation again on the cut version and see what minus forty per cent does. It usually breaks. The point where it breaks is your padding line: above it the poem has room to move, below it the poem loses information. Most writers find their useful band is between minus fifteen and minus twenty-five.