As many members have already pointed out, both RC and CR are difficult to teach because the skills necessary to do well in those sections are highly subjective. I think the books, such as Kaplan
or Manhattan, can teach you the basics, but it ultimately your success comes down to your inherent ability.
I would suggest that you go over many question types and look for patterns in your errors. Learning by doing is a great way to develop your skills. Use this forum. I found that by participating in discussions, answering questions, and letting others look over my answers, I learned a lot more then by simply answering questions from a book.