Stranger in a Strange Land
I read something recently that suggested this. It said that to become a better writer it helps to become a better reader. It gave several suggestions on ways to pay better attention to the words and the structure of the sentences and it said that when a particular passage strikes you to write it down and then write a small something about it.

Having enjoyed a few other books by Heinlein, I picked up Stranger in a Strange Land a couple of years ago. It has sat comfortably on a bookshelf waiting for its day. Last night, I finally got around to it.

"Oh, I admit I don't go to church much, but I was brought up right. I'm no infidel. I've got faith."

"Good. Though I've never been able to understand 'faith' myself, nor to see how a just God could expect his creatures to pick the one true religion out of an infinitude of false ones- by faith alone. It strikes me as a sloppy way to run an organization, wether a universe or a small one. However, since you do have faith and it includes belief in your own immortality, we need not trouble any further over the probability that your prejudices will result in your early demise. Do you want to be cremated or buried?"

I loved this whole scene. Jubal is trying to talk Duke out of making judgements on other cultures based on his own beliefs. This particular passage made me really feel more connection to Jubal Harshaw. His reasons for never understanding faith mirrored my own. This is one of the reasons I think I enjoy reading Heinlein so much. He makes you think and sometimes I recognize some of my own thoughts in his characters, so I feel more connection with them.

Two pages later:

"I didn't get any 'training at my mother's knee' not to be a cannibal. Hell, I didn't need it; I've always known it was a sin--a nasty one. Why, the mere thought of it makes my stomach do a flip-flop. It's a basic instinct."

Jubal groaned. "Duke, how could you learn so much about machinery and never learn about yourself a tick? That nausea you feel--that's not instinct; that's a conditioned reflex. Your mother didn't have to tell you, 'Mustn't eat your playmates dear; that's not nice,' because you soaked it up from our whole culture--and so did I. Jokes about cannibals and missionaries, cartoons, faerie tales, horror stories, endless little things. But it has nothing to do with instinct...because cannibalism is historically one of the most widespread of human customs, extending through every branch of the human race. Your ancestors, my ancestors, everybody."

Besides Jubal's debating style and ideas, I love the natural dialogue. In this whole scene the dialogue between the two characters seems very natural. The sentences aren't always completed or properly structured as it would be if you were writing some thesis.