Lately I've begun to see how words in a book ought to be invisible. The meaning should be visible, but the words should be like clear glass: transparent to the reader.
I like it when I'm a reading a story and I don't notice the words. It means I'm immersed in the story's world. But if I'm reading, and the words trip me up, I've lost sight of the meaning. The window into the story's world is smudged.
Words should be humble. If the grammar gets in the way, it's no good, even if it's correct. If the words are grandiose or cleverly crafted to be poetic or literary or intellectually impressive, and they obscure the meaning, they're no good. I don't mean that big words are inherently bad, but they ought to be precise words, to serve the meaning, and not be a big thumbprint on the story.
So, I'm now trying to be a window washer. :)