If you are studying on your own, the Princeton Review combined with the materials published by the GRE test company are the way to go.
That's what I did. Princeton Review books for preparation and published GRE tests for practice and self-assessment. Of course, I did this almost 25 years ago, so this is less advice than reminiscence.
I'm not familiar with the Biology subject tests. For the Psychology subject test, I reviewed a couple of general psych textbooks and my notes from various survey-level psychology classes.