Dear Sir,
I suppose you are referring to GRE General Test right?
Personally, I found that it was sufficient practice to buy the book (by ETS) and work through their sample papers. (I took the test in 2011)
Also, due to many applicants from China and India, now the Maths test (Quantitative Reasoning) is getting harder to score, while the Verbal Reasoning and Analytical Writing is getting easier (average score being pulled down by applicants from China and India). These are my personal opinions of the GRE.
For GRE Quantitative Reasoning, speed is really a major factor, so much practice is required. Also, it is good to know American Math terms like distances using feet, etc. Also, one needs to get used to the computerized system, and the GRE computer calculator. Knowledge of the marking scheme is also essential, for example, it is ok to write fractions without reducing it to lowest terms.
Also, now there is a policy that one can choose the best score to send to instititutions, so no harm taking more than one test, and choosing the best score.
I also tutor GRE and SAT (math section).
Hope it helps.
Best regards,
William
Maths Tutor
http://mathtuition88.com/