RC used to be a HUGE problem for me as a kid. so when i prepped for the gmat, i spent extra time on this section. on my three gmat attempts, and my GMAT prep practice exams, i didnt miss a single RC question (bought the ESR reports, scored 51 each RC, was able to check practice exams) .
here is what i did. two things you absolutely must know: what is the main idea of the passage, what is the passage structure. if the passage is a single paragraph, you can probably just read the whole thing. if the passage was longer, i would take notes.
para 1: main idea
take a few notes on some important ideas, names, etc. look for signal words, like however. if a passage says dogs are great, then the next sentence in the passage says however, you automatically know the next sentence will be the opposite of what you just read. being able to predict what the author will say can greatly increase your RC speed and understanding of the passage.
i never read the whole passage on long questions. if the questions ask for something specific, based on a my understanding on the passage structure, i should know where to look for the answer. only when the question ask me to read in detail, do i actually pay attention to the specifics. example, if half the para discusses why dogs are great, on my initial read, i skip over it, i just write end of passage 1, dogs are great in my notes. when the question ask specific reasons why dogs are great, i then go that the section of the passage and read in detail.
hope my rambling helps you in some way. feel free to ask me any questions