Often, native speakers rely on their ear to solve Sentence Correction problems. This will get you to a certain point, but you may not be able to make the subtle distinctions necessary to get down to the right answer on a tougher question. My experience is that both native and non-native speakers benefit from working through our Sentence Correction book. After each chapter, you can follow up with targeted problems in
the Official Guide. (When you get the book, you also get access to our categorized problem lists.)
I can give more specific advice if I know more about your case, but here are a few tips:
1) Ignore your quant and verbal test percentiles. Just look at your subscores. Both quant and verbal are scored on a 51-point scale, and that's what you should use to compare your strength on the two sections. Unless you are *much* better at quant than at verbal, your quant percentile will be lower, but that's just because people who take the test tend to be stronger in quant. Again, look at your subscores to compare. Unless one score is a whole lot higher (8+ points), you should probably split your time 50/50 between quant and verbal. If one section *is* much stronger, you can shift up to 2:1 in favor of the section that needs more work.
2) Commit to changing how you do things. Don't just accept that "either I can read or I can't." Think about which of your habits are helping or hindering you. Work on strategies to stay more focused during reading. Don't get in the habit of reading things without making sense of them.
3) Practice a little every day, and spend the majority of your time reviewing and redoing problems.
Let me know if I can follow up with details on anything. Good luck!