For SC, it's a matter of having a good grasp of the grammar tested on the GMAT, for instance, modifiers, pronouns, parallelism...etc. Once you have a solid understanding, SC shouldn't be a major problem. The manhattan sc book should help you with the groundwork and the rest is pretty much up to you as it's practice that makes perfect.
For RC and CR, it's really a matter of preference and technique to understanding the passage. Some like to skim and read only the first line of each passage, and there are others who takes notes along the way as they read. For myself, I read everything with pauses in between to absorb what I'm reading before I go and tackle the questions. Take a few passages out and try out the different techniques and find one that suits you. Once you're done, keep using that technique for your daily practice. With more practice, everything should be fine.
Lastly, you will want to build up stamina and address timing issues. Use a timer to help you with that. I was going at 25 SC, 10RC and 10CR everyday at a certain point. It helps your body adapt to tackling a string of verbal questions at a go...