One way to write an interesting essay on the imagery used in John Donne’s poetry might be to choose a random sample of poems and a random sample of images. For instance, you might choose the first five or so lines of the first five poems by Donne that appear in a standard anthology of poetry.  The first five poems in the Donne section of the latest Norton Anthology of English Poetry, for example, are the following:

• “The Flea”: The first six lines focus on imagery of a flea sucking blood from a woman after it has just sucked blood from the male who is courting her:

Me it sucked first, and now sucks thee,

And in this flea our two bloods mingled be . . . (3-4)

• The imagery here is surprising, unconventional, attention-grabbing, and provocative. One wonders why the male is using this particular imagery to attempt to court the woman. He is evidently good at improvisation (as the rest of the poem also shows), and he also seems confident of his ability to make a convincing argument no matter what “raw material” he is given.
• “The Good-Morrow”: The first few lines of this poem compare two lovers, before they met and fell truly in love, to unweaned children who “sucked on country pleasures” (3)  and also to the seven youths in a Christian legend who slept for 187 years. Here the tone associated with the imagery is both humorous and humorously crude, especially in the use of the verbs “sucked” and “snorted.” The speaker here is using imagery to show his cleverness, his wit, and his geniality.
• “Song: Go and catch a falling star”: The first five or so lines of this poem are particularly rich in various images, showing the speaker’s inventiveness, wide-ranging mind, quickness of thought, and love of intriguing ideas.
• “The Undertaking”: The opening lines of this poem use an allusion to the legendary “Worthies” (three Jews, three pagans, and three Christians), suggesting (as in “The Good Morrow”) the speaker’s learning, cleverness, and wit.
• “The Sun Rising”: In the opening lines of this poem, the speaker uses the conventional imagery suggested by the title, but he uses it in a thoroughly unconventional, witty, and clever way. This speaker, like some of the others already mentioned, is self-confident, assertive, and full of intellectual energy.

Donne’s various uses of various kinds of imagery, then, can tell us a great deal about the speakers of his poems as well as suggest a great deal about the tones and possible meanings of his works. Perhaps the strongest impression left by this little survey of Donne’s imagery is of the sheer variety of the imagery he is capable of using and thus of the breadth and depth of his own mind.  Rarely is a Donne poem predictable, either in its imagery or in its development and meanings.