As I am slowly and painfully learning marketing (through marketing my own book), one fact is hammering its way into my head: writers depend on word of mouth. Yeah, there are a bunch out there that get big publicity, maybe through their publishers and maybe through some fluke. But most writers, whether they self-publish (now called "Indie publishing," as in "independent") or are published by traditional publishers, are left to get the word out on their own.
So. . . in the interests of good karma. . . if I liked it, I'll share that. Tell a friend who likes the same sort of thing. Post a review, here and on Amazon. If I ever figure out that whole Facebook fiasco, I'll mention it there. Even if the author is pretty well known, but especially if I've never heard of him or her before.
The jury is still out on what I'll do about books I didn't like. For one thing, since I'm trying to read more books, I am going to work on learning to stop when the pay-off isn't there. When my interest goes, I may read some reviews and comments (I was prevented from giving up on the 3rd book in Naomi Novik's Temeraire series by people who assured me that it would improve, and that the next book in the series was better. The book did end better than it had looked like doing), and if I don't see a compelling reason to continue, I hereby resolve to cut my losses and go read something else. Of course, if I don't finish a book, I can't review it. Which gets me off the hook, because I really don't want to say mean things about anyone's work. Not even when it deserves it.