It's a tough test but not an impossible one. It's scored differently than other standardized tests. The harder questions are towards the beginning. If you can answer those correctly, you're chances of getting a higher score are good. Also, the next question is always based on how you answered the previous question. So basically the questions on the test are "customized" to your capabilities. It has a different algorithm to it, any GMAT book will help explain it.

With respect to GMAT practice books, I would recommend the official GMAT book published by the MBA. If you're well versed with the concepts, I would suggest taking full length computer based practice tests as opposed to practicing in on paper. There's a whole lot of difference there. Timing is all that matters if you know your math and Grammar.



Good luck!