Read the Princeton Review Guide. "Cracking the GRE Literature in English Subject Test," published by The Princeton Review, is widely considered to be the definitive guide to GRE preparation. The book should be available at your nearest library but if not, it can also be purchased online. Be sure to seek the most recent edition.
Study a Norton Anthology Literature Collection. The GRE Literature Test focuses mainly on canonical works that can all be found in any Norton Anthology Collection, particularly the British literature editions. Read the introductions very closely to each author in the anthology but don't spend too much time on each individual work.
Take the practice test. When you submit your application for the GRE Subject Test in Literature, you will receive a welcome packet that includes a practice test. Take this test after you have had a chance to read through the Princeton Review Guide or any of the Norton Anthologies.