Have you gone over the Foundation/fundamental books? If studying for the three specific types (SC, CR & RC) is not producing meaningful results, then you may need to step back, buy a good grammar book and start going over the basics, that should in theory help you improve your Sentence correction, CR & RC ( an improved "basic" grasp of English should translate to smoother understanding of the Question stem, and passage). You should also look to read good English, from journals, books, business publications etc to develop the habbit of reading heavy material. Reading well written literature will also assist you in spotting grammar errors when you are faced with Sentence correction.
"When you want to succeed as bad as you want to breathe, then you'll be successful." - Eric Thomas