The basics, as taught in PR, Kaplan, Manhattan guides are worth a careful look. Honestly, all I did was to learn these carefully and improved my verbal from high 30's at the start to 45 on the real test (And as a result improved my score from about 700 to 770).
Specifically, there are the SC rules. Subject-verb agreement, parallelism, tense, etc... Learn these, and learn these well.
For RC: develop your own style of annotating to get a sense of the whole passage. At the start, I'd just read the boring passages, retain nothing, and have to scramble to figure anything out. Sound familiar? Outline! You don't have to make it pretty, and there is no set style, but I believe that nearly everyone needs some crutch to get them through these boring passages.