<human>: Can you give me a shortened version of the text?

Well I have noticed that when reading a book, poem, excerpt I have a hard time analyzing it ie. What is the idea, augment, mood? An example is when I was reading The Great Gatsby. We were asked to analyze the text in chapters and underline anything that was important. I would either underline something that wasn't very important, or I would underline something important but not understand why and not be able to understand the author's argument. I understand something after it is pointed out and I can connect the evidence to a thesis however, IM VERY BAD at initially pointing things out or gathering an idea and finding evidence for it. So, My question is: How can I improve my analyzing skills to understand arguments/ create thesis's?
<bot>: I'm very bad at analyzing text, specifically finding the authors argument. How can I improve my analyzing skills to understand arguments/ create theses?