Do not, for a moment, treat this like a test for which you can sufficiently study. By study, I mean learning or reviewing actual literary material en masse.
This test is absurd. I've said it, my friends who are now PhD candidates have said it, and my professors have said it. It is glorified trivia. It barely reflects readiness for doctoral level study in literature. It does not require you to write, or to synthesize information. It merely asks you to remember random tidbits about everything that's ever been written across the entire literate planet since the Middle Ages.
A question I remember clearly: "Which of these authors was not employed in a non-literary profession prior to their first publication?"
Speaking as someone who already completed an MA in English: This question is not remotely related to skills you need to have or work you do in graduate school. We don't work like that. We're not generalists. The idea of that is absurd. And one of the first questions on any doctoral application to an English program asks you to designate your topic of interest.
The percentage of actually relevant questions on the GRE Lit test is, I dunno, maybe 5%?
All that said: yep, you sure do have to take it to qualify for many programs. When you take it, I guarantee you will stare at the first page of questions and say to yourself, "Are you kidding me?" This feeling will persist until you finish, and then you have to address the persistent voice in your head that says, "Dude, just light your answer sheet on fire, honestly. And then maybe yourself."
It's not that it's hard. Hard is not the issue here. It's not a matter of intelligence. This isn't a matter of successfully coding a computer program; it's not testing your skill as a writer or a reader. It's simply a matter of the truth that few humans are capable of having a broad enough catalog of memorized tidbits--obscure, esoteric, trivial tidbits--to excel at this test.
Do not for a moment attempt to endow yourself with a superhuman and exhaustive encyclopedic knowledge of the Norton Anthologies, all of the critical theory disciplines, all of the authors and their lives and the bad historicism that the GRE is evidently besotted with asking about, or memorize Shakespeare's catalog. I'm not saying this was your plan, but if anyone tells you to do this, punch them because they hate you and are trying to kill you.
Get yourself a nice test strategy book from Kaplan and learn the tricks, because that's what the GRE is about. It's not about knowledge, it's about logical thinking and strategy. Remind yourself that English programs know this test is looney, and probably most of the admissions committee thinks it's frigging looney. There is going to be a threshold that, if you fail to meet it, they would have right to be concerned. But trust me when I say, from what my professors on admissions committees told me, they know this test is the devil, and they don't expect perfection or anywhere close.
Good luck. Strategy, not rote memorization. Buy the book, learn what they're likely to test on in 2016/2017, focus on those areas, review your crit theory notes, and try your best.