Having taken up GRE/TOEFL/GMAT in order, I realised that more you practice with sample tests, better your score in the exams. Voracious reading of general articles(the one like The HINDU editorial page) will help you in RC, and for Math, get your basics strong, CSR Competition Success Review will get you on the right track.
I keep reiterating, practice as much as you can, a daily 3hr practice test(follow religiously the time allotted for each section) WILL DEFINITELY BOOST YOUR SCORE.
