It's been a while since I took it (before online resources were available), but I found that taking practice tests was helpful, and really pretty sufficient.
I'm not really sure what advice to give on the verbal portion - as I recall it was pretty similar to the practice tests that I'd taken - lots of vocabulary, and the typical "read the paragraph and answer questions on what it means" type of stuff. I'm not sure how much you can really study for that - memorizing words just isn't too efficient - there are too many. Latin/Greek, maybe?
On the math and analytical portions, I found that it wasn't so much that things were hard, or difficult to figure out how to approach, but that the time limit for the exam just wasn't sufficient - it was more a question of how many problems you could do correctly *fast* than how many you can figure out. The practice tests really helped here - the problems seemed to fall into the same set of categories on the real test as on the practice ones, so it definitely will give you a good idea of what to expect, and which problems, if any, to simply ignore as time sinks - you can come back later if you get through the whole thing. As I recall, lots of geometry/trig/algebra type stuff on the math test, and tons of logic puzzles on the analytical portion.
On the subject portion (mine was biology), it was pretty close to the practice exam - I'm sure they vary wildly among the subjects. There was no writing portion when I took it.
Anyway, like I said, it has been a while, so things may have changed - but I thought that practice tests (and time yourself while doing them) were a good investment. Oh, one more thing - make sure you get a good night's sleep beforehand... I wound up having to drive a ways to get to the testing center, (due to procrastination in registering, and finding out that the deadline was "tomorrow" - hmm... I had to drive an hour to get to a FedEx pickup point that could even get my materials in on time - sorry, tangents

) and getting to town the night before and staying in a hotel helped. Anyway, I hope that helps

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