You won't see significant score improvements unless you work on verbal. Ideally, you want to focus on that area, but without totally neglecting quant.

You haven't mentioned your weak areas. However, there are a few books I can recommend. If you want a general book, try Kaplan Premier. It's got some of the more common aspects of the GMAT and quite a few practice problems. For SC, most people recommend the Manhattan SC guide - it doesn't have any practice questions (or so I understand), but the grammar review is stellar. For CR, you might want to try the PowerScore CR Bible. PowerScore is well-known in the LSAT world and LSAT is basically a tougher version of the verbal. You might also want to try and work on your general English by reading some quality material like famous American journals.