I'd credit this if I could, but I can't remember who said it: Give readers just enough clues to figure out the next step or the answer to a problem in your story just before the characters do. It makes the readers feel smart and keeps them engaged.
I think this is great advice, although I don't know that every book needs to follow it. What I do know, however, is how far it can go wrong if you can't judge what "just enough" means. I'm reading a story now by an author I usually enjoy, and it's taking the characters so long to figure out what's going on I'm beginning to think they're stupid.