I got a 680 the first time I took it with a low score in quant. The only preparation at that time was the 2 ETS tests...
This time I only concentrated on quant and got a 710 (49 Q 36 V). I did all quant OG questions. 4 Kaplan tests(570, 530, 590,590) and 3 Princeton tests (640,660,690). I reviewed all quant errors and that's about it.
The probability and combination questions I had were pretty easy, so dont stress about it too much.
The verbal section had a killer 90 line RC. Thats what took all my time...