I can offer something on SC, since it was my weakest area but I became strong…
When approaching a SC question, I’ll write A – B – C – D – E on my paper, and as soon as I can eliminate a choice, I cross it out and only focus on the others. (Just be careful that you’re eliminating choices only for valid reasons.)
I became good at SC when I learned how best to eliminate choices. You’ll notice a pattern among all the answers. For instance, two of them may use the pronoun it, whereas the other three of them may use they. Once you see this pattern, then you know exactly what they are testing you on. Figure out which group is right, cross off the ones that are wrong. You’ll usually see 2 or 3 or concepts being tested, and there is always enough to direct you to an answer.
I would spend a few days of doing the above with the official guide, noting the concepts you are iffy on and studying those concepts ‘till you know them cold. Once you have completed 90 – 100 SC questions in depth, go through the
MGMAT SC book and read it slowly and in depth. It’s a great book.
Finally, give those last 50 or so questions in the OG a shot.
One last note, the Kaplan 800 book helped me understand a lot too. If you have it, I’d run through their SC questions, which are very tricky. I did this before I did anything else, in fact. Their answer explanations worked well for me.
Oh yeah, and study each question in depth. It’s better to do 5 and understand them fully than to blaze through 50. Mark the ones you get wrong and always go back and refresh yourself on the concept.