I believe that it's quite difficult to obtain the "exact" main idea from the passage. That's why I pay close attention to eliminating 3 answers to get to that one answer all the time because I can def. look at ideas in relation to each other and see the comparisons of right and wrongs. So, I usually think "relative" instead of "exact."
Also, when I read paragraphs, I try to make connections between the first sentence that i read and the next sentence. I try to look at each sentence in relation to each other (ex. usually you'll see a main point at the beginning of the sentence (not all the time) and then you'll see the supports throughout the paragraph). Each sentence or idea seems to point a direction towards what the main idea is. Sometimes this is tricky. For example, the beginning of the sentence may start out talking about events that led up to a war but then the rest of the paragraph talks about the weapons used in the war. So, obviously the main idea has more to do with weapons of war instead of the events that led up to it.
So when I read main idea questions, I always ask myself "what did the author spend his/her time talking about the most?" The author could have picked "any" direction but they chose that specific direction. So, as you read the answers, you'll start to eliminate answers because "this wasn't what the author spent most of his/her time talking about."
Instead of calling it "main idea," I kind of like to call it "direction" that a passage takes. Warning though, Just paying attention to the structure isn't good enough, you have to really say to yourself "ok i'm going to focus and concentrate on this specific passage and try to comprehend what this author is saying." Usually when I work on verbal, I feel very uncomfortable in that I try to zone in and focus entirely on the passage that I am reading. Like someone said on this post, verbal is like working a muscle in that you have to work it out frequently and even push it further to improve. I'm counting on this basic idea over any other tricks that I came up with. I've tried highlighting, writing a few sentences down to summarize paragraphs, and even assumed that you could work your way through finding the wrong answers by studying the type of wrong answers. These little bitty tricks don't do you any good in that they sometimes steal attention away from comprehending the passage. Although I do see the value in spending a few seconds processing what you just read as you read the passages.
hm... ok i wrote too much... but that's my opinion of the main idea thing.
