(i.e. What kinds of words did the author use at different moments and what are their effects on the reader?)
Donne's poem "Death Be Not Proud" is really an 'in-your-face' kind of poem. He deliberately chooses very strong adjectives like "mighty" and "dreadful" to describe Death in the opening of the poem only to turn around and recant those words in the same line. It's a slap in the face of Death.
This question might get a more detailed response if posted on the Q&A section.
The first thing that came to mind when I read your question were the lines,
Thou art slave to Fate, Chance, kings, and desperate men,
And dost with poyson, warre, and sicknesse dwell,
Here, the poet is using personification by speaking to death itself. The most important word in this section is "slave," because the poet is bringing death down a notch. Death is, in fact, used by Fate, Chance, kings and desperate men. We don't usually think of death as a slave, but as something that wields power over us. Donne's word choice gives us a new way of looking at death.