I’m probably not the most representative person to answer this question since I’m someone who does well on standardized tests. I prepared by buying a couple of GRE books and using them to review math I hadn’t seen since 9th grade and get familiar with the test by taking a few practice exams.
But the amount I studied isn’t relevant to how much you (or anyone else) should study. That’s something you need to figure out on your own. My recommendation is to find out more about the GRE on their website, and buy a book to take a practice test. From there, see how much you need to review/study and decide if the books are enough, or if you want to take a course. Many colleges have GRE classes, and there are several companies that hold them also.
Good luck studying!