I did really well on the GRE and used Kaplan's Premier as my main guide. I also went through the ETS guide, which was helpful for finding out all of the content that could appear on the test, but I found Kaplan had better strategic advice than the ETS guide did. It was nice to take the ETS Guide practice tests, because they were very similar to the real test. I also read through the book "Word Power Made Easy" by Norman Lewis, which was written several decades ago and can come off as rather dated, but was incredibly helpful to me for the verbal section. It turned out that quite a lot of words from that book were on the test, and the book has lots of interactive exercises and stories to help you learn word roots, so it's not just memorizing. It starts out very easy and progressively gets more complex. I also used Kaplan's vocab cards, which I would also recommend. Good luck!