When you sign up for the test they send you a couple free practice tests. Just go through one of them once, it doesn't take long. Don't have to buy a book or anything unless you want some more review.
Since I had been out of school for several years it was good for me to review it, so I just did a couple of the practice tests. Did great on verbal (690 I think, which was like 96th percentile), and ok on quant (760, which was like 88th percentile... really should have aced it but oh well. Don't think they told me what I missed, but it was probably something stupid).