Each word is there for a purpose. Are the two poets using different words to express the same emotion or idea or picture. Are there words that have their own specially nice sounds. The verse by Milton below has lots of long vowel sounds. Watery sorts of sounds.
Alliteration is a way of putting words together that have some of the same sounds.
Milton used it in this verse from Comus. You could compare the imagery the two poets use. It can be very effective to describe something by actually describing something else - or saying something is like something else. The poem's voice Lastly, you need to think about each poem's voice. Looking through my poetry books, I was struck by how few women poets were published in the past.