Over time, I have come up with the foll. strategy:
Write down the mapping of the passage....how each paragraph begins, the gist of it(how it flows in a couple of words), the authores tone, making a special note of words like: 'usually, therefore, in so and so's opinion, etc-> see Kaplan
's book for details.....and it quite works!
IMHO, your strategy should evolve with practice, I do like Kaplan
's methodology in particular for main idea of the passage, and there is no substitute for practice!