It's one of these strange things where once you nail it you'll wonder why it was hard.

What i'll say is it's all about close reading. Pick a passage. Read it carefully. Take note of certain things - things that appeal to you in the passage - then ask why they appeal to you.

If a certain emotion is invoked, try to persue why. You'll do it once, then all of a sudden you'll be doing it. Be warned, it can be hard to put down - there are some great books that don't have anything much "swimming beneath the surface" - Lord of the Rings for example is more history than allegory - and picking writing apart may make you enjoy these wonderful "natural" books less.

Always say - why, how. And you're doing it.