The GRE Literature exam will assume that you know the basics of several prominent schools of 20th-century literary criticism. They can be divided roughly into three major groups, as follows (with more information if you follow each of the links):
Marxist Criticism- Identity Criticism
- Historicism & Sociological Criticism
Linguistic Criticism- Formalism
- New Criticism
- Structuralism
- Post-Structuralism & Deconstructionism
- Reader-Response Criticism
Psychological Criticism- Freudian Psychoanalysis
- Archetype/Myth Criticism
If you didn't get a lot of theory as an undergrad, it's worth adding at least one short theory survey to your reading list for the GRE Literature exam. I recommend Culler's
Literary Theory: A Very Short Introduction. It's short, but enough to get you through the exam.
If you have the time, though, every aspiring grad student in literature should read
A Reader's Guide to Contemporary Literary Theory. It's a little more thorough.