It took me awhile to learn something, when I first experimented with writing novels. Readers aren't stupid. And my over-explaining, my telling-instead-of-showing, my overuse of adverbs, etc, was treating them like they were. I just didn't realize it.
I found a great blog post today by Kristin Lamb, and I agree with 100% of it. It's a must-read for new authors, as well as a good reminder for those of us who've been around the block awhile. Link here
And here's a link to an earlier post of mine, talking about this Readers-Aren't-Stupid issue. I think it's crucial that writers find the balance between offering information readers must have, but not hitting them over the head (treating them like they're stupid) with information they don't need. It's tricky, but if we become aware of the pitfalls, we can avoid them.