This a very broad question, so I'm not sure I can effectively answer it in a forum post. I can give you a general overview of the PowerScore method, however. We use a system called ViewSTAMP, which is an acronym standing for:
All of these elements should be identified and marked during the first read-through of a passage. Try not to take too many notes, as that will slow you down and may confuse you later on when referring back to the passage to answer the questions.
Make sure you track all the viewpoints expressed, including the author's, and where they are in the passage, as well as what their different arguments put forth are. Tone is important to note whenever it deviates from objective, neutral language, as it's key to understanding the author's attitude towards the subject and any potential inferences you may be asked to make based off of said attitude. Finally, the main point is analogous to the conclusion in the stimulus, although usually found in the first or last (or both) paragraphs. I would also add that it is important to also keep in mind what kind of source this may have come from, and always be able to answer the question "Why was this written?" after reading a passage (i.e. know the purpose behind writing the passage).
If you'd like a more comprehensive explanation of the PowerScore method of attacking Reading Comprehension, the RC Bible is available here
Hope this helps!