The crucial part is the idea-finder, but I didn't learn and can't teach it.

I have access to a pile of books to teach this to kids, and have used them. It's the number one skill that children doing poorly in reading comprehension must be taught. One of my favorite exercises related to this is. "Here's a paragraph. Find the sentence that is not on topic." Usually the sentence does seem tangentially related to the topic, but once you can concisely put in words the purpose every other sentence has been bent toward, it stands out like a sore thumb.

It's not fun, exactly, but studying SAT/ACT reading comprehension problems also helps on this front. There's probably five or more questions on every SAT/ACT that only ask "what is the main idea of this passage?"