Since you have already taken the test once..i assume you must have done a few full length tests...What were your scores in those?
Manhattan SC is the best book out there for SC. IMO, if you are not a native speaker, like me, you must have a lot of notions, hunches, which are not always in sync with the rules of english grammer. This is the reason why you should stick to the rules and not go jsut by your hunch. I have had a tough time too with the verbal section. My 2 cents - Stick to the rules in MGMAT SC
and vigourously and reliogiously read the explanations. Make a note everytime your hunch disagrees with the rule. FOLLOW THE RULE. MGMAT SC
has proven and evident history of bringing up SC scores for 99% of the crowd here. If you have time, go through that book at least twice before your test. And not just read like a novel, it is a pretty interactive book and needs your constant involvement and homework in terms of solving the OG 12
questions at the end of each chapter. Once you have gone through the book throughly, each SC question should start to present itself in a manner that you can say - "Ok, this is parallelism, modifier problem etc".
SC is very much like a quant problem. Once you know the problem, you have the solution right in front of you.
For RC, there are many strategies available. However you have to really work on creating a strategy of your own that works best for you. This may be one of the available ones or a combination of 2 - 3 different strategies. What worked for me was the approach. I approach each RC as something new to learn from. It takes me a good 4-5 mins to read the passage but after spending a good time, I know most of the content and when the questions pop up, i know where to look for the details.
All the best!
Time to play the game...