It's actually pretty simple my friend. Finding the main idea is easy while reading as long as you keep this in mind:
The main idea is found by analyzing what the main topic of the story is. For example, if a movie is talking about dogs for 15 minutes, and only talking other animals for 5 minutes. That means that the main idea is the dogs. This same analogy applies to reading. Whatever is being talked about the most, is the main idea and topic.
