This book was extremely helpful, and I would suggest that you don't wait to read it. If you're planning on taking the GRE ever, start preparing for vocab now.
The book starts with general approach, which is really quite helpful. I really feels as though I am prepared for each sort of question. Before reading this I would have had no point from which to start with many questions, but this guide helps to focus your attention on what you should be studying, helps you to understand how to approach questions, and if you come to a question that you're not prepared for, the guide helps you to eliminate bad answers (for instance, words with no antonyms are obviously not the answer to and antonym question).
I recommend this book to anyone with even a vague inclination that they may one day take the GRE. Start preparing now!