Verbal is definitely the hardest to improve. Having said that, I agree with the advice to disregard the test prep companies' advice (except for exam krackers). That is to say, don't try any gimmicks. Read the passage from beginning to end FOCUSED. I found that focus and mental clarity were the most important aspects for me. Trying to skim the passage, then read the questions or w/e Kaplan advises just left me scrambling. If you pace yourself, you have like 8 minutes per passage. Reading the passage carefully only takes a couple of minutes - and it will greatly assist in remembering the finer details, main points, tone, and layout of the passage. If you need to find a specific detail, you will have much more success this way. Also, the answers tend to be rather tame (e.g. cautiously optimistic vs condemning etc), so you can typically rule out a couple answers immediately. Any question asking you for conclusions from the passage will be extremely literal. There will be trap answers that seem like a logical inference, but only because you may have a personal belief or value regarding the topic. So another key is to read the passage completely unbiased. Take what the writer says as fact, and try to follow their logic.
Perhaps a slightly radical approach, but you can practice by reading viewpoints of people with whom you disagree (to get the detachment down), and really stale and boring articles (to get the focus down). Its tough to stay objective when reading a passage about murdering kittens, or focused when reading a passage about suit fabrics.
The Princeton Review Hyperlearning Verbal workbook is an EXCELLENT resource, and is commonly sold on SDN.
tldr: Practice reading the passages intently without drawing on outside experiences and beliefs.
