The most important thing about RC is understanding what you read. Being able to read fast is also important, but remember that speed is always secondary to understanding. Below are some tips for exam-preparation as well as for general improvement.
Don't rush yourself. It is natural that you will start a little slowly and then build up speed as you gain familiarity with the passage.
Read all the questions first (if the exam format permits this). This will help you zero in on the relevant portions when you start reading the passage.
Read actively. This means, try to anticipate the next sentence. Reading this way will help you engage with the passage more closely.
Make notes to capture the essence of each paragraph within the passage. The first sentence of the paragraph usually conveys the main idea or theme of the paragraph.
Don't try to memorize anything. Memorizing consumes time and is not very useful.
Practice a lot of Reading Comprehension questions online from sites like
www.lofoya.com/Verbal-Test-Questions-an ... /intro.htm ,
www.rhllschool.com for free.
all the best!!