This is going to be a short bit. I don't believe that every rule is meant to be followed without exception. When I was younger, I remembered reading somewhere that one should never use contractions except in dialog. My writing was a veritable desert. So formal and stodgy.
So when King says that adverbs are the devil, I give him a nod and quickly move on. His advice about passive voice is solid. People enjoy reading books about people who do things rather than books about people to whom things happen. And the dialog tag is also solid advice. If you've written your scene properly, then you should rarely have the need to use anything other than the solid tag "said."
But the main thing I took from the section about passive verbs and adverbs and dialog tags, was about timidity and fear.
A writer may be a lot of things, but he must never be afraid. Not of parents, not of librarians, not of reviewers. And certainly not of his own words. A writer must not be timid. He (or she or course!) must be bold. Must take chances, even if conventional wisdom says that it's wrong.
Being a writer is all about taking risks. Every single word that makes it to the page must push the boundaries. It must be heartfelt and beautiful and terrible and bold. There must be nothing safe about your books or about your words.
Every adverb should be an act of defiance.
In the end, it's not about adverbs or dialog tags or passive voice. It's about knowing what you want to say and being brave enough to say it.