You won't know until you take the test. Well I didn't know until I finished taking the test and got my scores. I scored 1380; 800 in Quantitative and 580 in Verbal. I am of the kind who does not care to devise smart strategies to take the test. I'd rather study 100% of the material I have and would grab more from any and all the sources I can find. So for GRE, I studied
1. Barron's Essential Words For The GRE : There really isn't any need to rote the humongous word list from Barron's GRE. You will do good with the Essential Word list which consists of 80 word lists of 10 words each with example sentences. I knew all the words that appeared on my GRE.
2. Barron's GRE Edition 2008 : Good for the Quantitative Section. It gives a comprehensive revision of Math Strategies required for GRE coupled with Practice Exercises.
3. Cracking the GRE 2008 : The Princeton Review : Good for Vocab and Analytical Writing. Has 4 Hit Parade Lists and 2 Beyond Hit Parade Lists. I must say, they have done a extensive research in building these lists. It helps to concentrate on a list of most probable words than to rote the extraneous words from GRE Barron's which you might end up messing with. Also, it has sample issue and argument essays. The DVD that comes with this book tells you the strategies to take the GRE, the most important of which is to keep in mind that it is a Computer Adaptive Test so you do good by starting strong because the first 10 or so questions of each section weigh the highest and determine a good percentage of your score.
And for the Issue Essay, downlaod the pdf from here . This site has many more GRE preparation materials. Go through them if you have enough time.
Most importantly, do not miss to take practice tests before going for the real one.