I forgot to add that you can learn a lot by writing your own critiques of things you read. I ran some of my work through the Critters website (no, it's not zooish, and they probably wouldn't much like that)--it's at critiques.org . It's a place where you can get your work critiqued by other writers in exchange for writing your own critiques. I recommend it.
And, you can get enlightenment by reading reviews. Before I decide to buy any new book, I go to Amazon and read their one-star reviews on it. The reviewers who hate the work are often quite precise about why. One of my favorite examples is Ringworld, by Larry Niven, maybe one of the all-time worst writers who ever got famous. Check it out.
