Read, read read and then read some more. As far as practice passages are concerned, AAMC >> everything else. I think TPR's CARS stuff is pretty good and is slightly more difficult than the AAMC material.
With Verbal I think there are three keys to success: 1. Timing. 2. Having a good testing strategy and being familiar with the way questions are asked and answers are framed and 3. Having strong reading comprehension and verbal skills. 3 is hard to develop in a short period of time (ideally one would be developing this skill throughout their entire education). 1 and 2 can definitely be mastered.