John Milton (1608-1674) was a major English poet and writer of the Commonwealth period. He is guaranteed to show up on the GRE Literature exam.
His two most important works are also his longest & most famous:
1. Paradise Lost
-Distinctive style: Latinate, syntactically-complex, heavily-enjambed blank verse
2. Areopagitica (treatise against censorship)
If you're doing any heavy reading to prepare for the GRE, and you haven't read them before, these should be on your list. You can get both in one volume if you buy the Norton Critical Edition.
Otherwise, you can rely on summaries and a sense of the styles of the works.
One or two of the following works may also appear on the exam. The poems listed in bold are particularly likely to show up. Read the short works at least once. For the long ones, simply read the summaries.
1. "On Shakespeare"
2. "When I Consider How My Life Is Spent"
-On Milton's blindness
3. "How Soon Hath Time"
4. "On the Late Massacre in Piedmont" (sonnet)
-An early masque; young girl seduced by supernatural being
6. Of Education
-A treatise in support of the liberal arts
7. Samson Agonistes
-Play; Hebrew Samson, after betrayal by Delilah
8. Lycidas (long--read excerpts)
-Most famous example of the pastoral elegy; to colleague Edward King
9. Paradise Regained
-The sequel to Paradise Lost; temptation of Christ; not terribly important