Main Idea or Topic
When you read, it's important to make sure you know the difference between the main idea and the topic of a story. The topic is what the story is about, or the primary subject. For example, the topic of the Harry Potter series may be 'witchcraft' or 'wizardry'. But that's not the main idea, it's not the big picture concept.
Looking for the Main Idea
As you read, it's always a good idea to keep an eye out for the main idea. The main idea may be easy to pick up in some stories, but in other instances, you may have to go digging for it. Luckily, there are a few strategies you can use to help you.
First, consider breaking up the story into smaller chunks. See if you can find the main idea in paragraphs, sections and chapters. Taking notes as you go is helpful as well. This way, you can look for any common themes between chunks. You may even see a pattern develop between events or character insights.
Second, look for any repetition throughout the story. If the author repeats similar ideas, events or conflicts, that's a pretty good clue! Back to the Harry Potter example, Harry encounters very similar conflicts throughout the series. He battles Lord Voldemort, he deals with teenage problems like first love and he goes on incredible adventures with friends. These things are pretty consistent throughout all seven books. Odds are, they have something to do with the main idea!
Third, try putting the main idea into your own words. Generally, the main idea of a story should not take you more than one or two sentences to explain. Anything longer than that means you've either missed the main point, or you're highlighting details that aren't necessary.