how to work on RC passages for greater understanding?

The best way would be to practice it without keeping any time constraints. Read the passage again and again till you don't understand it completely. After that try answering the questions. Your focus should be on accuracy. Once you start getting accuracy greater than 80%, you can start to keep track of time and should challenge yourself to reduce that timing every week while maintaining the accuracy. This will surely help as last year I used to get around 12-14 RC;s correct out of 24. This year till now, in 5 mocks that I have taken lowest have been 17 correct.