Here is a PDF version of the novel you can download for your own use. I recommend installing in either the Kindle app or something similar, as it allows you to highlight key passages as you read. Here is a direct link HERE.
This is a neat map I found--someone has marked all of the important locations which feature in the novel. It's really great for helping to visualize the locations.
As you read, informally take note of the following things for each chapter. Don't forget to note page numbers for easy reference later.
Chapter 1: Take Note of How Nick, Daisy, and Tom are portrayed...their personality traits (honesty, intelligence, kindness, etc.). Take note of the East Egg mansion and what kind of feelings or thoughts it evokes. Question for later: how is Gatsby similar to and different than the others?
Chapter 2: Take Note of how the Valley of Ashes is described. What kind of mood is created? Why do you think Fitzgerald describes this scene in such detail? What about Myrtle? How is she similar to Daisy? Different? Question for later: how does seeing Wilsons and the Valley of Ashes affect your perception of Gatsby?
Chapter 3: Take note of the party preparations--what purpose does including such a detailed description give? What about the party itself? What stands out to you about it? Take note of all of the rumors about Gatsby. Do any of them seem plausible? Why include these rumors? On the opposite end...what about Owl Eyes, in the library? Why include a moment like this amidst the party? And why show the winding down of the party and the drunk driving/accident scene? Also, after this chapter, what do you know about Gatsby? What don't you know?
Chapter 4: Notice how much (to what degree) does Nick believe Gatsby's account of his background. Note that this will vary as the tale unfolds. Question for later: How does this scene convey a different sense of Gatsby once you've finished the novel vs. when you first read?
Chapter 5: How has the "reunion" affected your view of Gatsby? Does his house (and shirts!) convey a feeling or thought about him? Toward the end of the chapter, Nick comments on Gatsby's dream--notice this when it comes up! Also...notice when Nick describes Gatsby as "bewildered." Question for later: How does this scene convey a different sense of Gatsby once you've finished the novel vs. when you first read?
Chapter 6: Who the heck is Dan Cody? He's important! Notice how he influences Gatsby. Notice how and why Gatsby changes his name. Notice how very different this Gatsby house party feels, and take careful note how Daisy and the other East Eggers feel about the party, and notice how Gatsby feels once the party is over. In the flashback, take very careful note not just about the burgeoning romance with Daisy...notice what ELSE Gatsby seems to be excited about at the same time.
Chapter 7: The weather!!! So important. Notice what it does in reaction to (or in tandem with?) the events of the chapter. Also, take note of the showdown between Gatsby & Tom--notice the shifting power as the showdown continues. Also, in the aftermath of the car accident, take note of what everyone is thinking, feeling, experiencing--especially Daisy, Tom, Mr. Wilson, Nick, Gatsby.
Chapter 8: What is most important to Gatsby at this point? How do you know? Take note of Mr. Wilson. What motivates him at this point? What is Nick's attitude toward Gatsby at this point? Find evidence! There is so much here!
Chapter 9: What seems important about the funeral scene? How does Nick feel about this? Do you have a different opinion than Nick in some way? What do we learn from Mr. Gatz? What does his anecdote teach or tell us? Notice Tom and Daisy (again) when Nick runs into them. How have they been affected by all of this? How has Nick been affected by all of this? And re-read the final page a million times. It's poetic, but a very relevant and universal closing for this story. What does that page convey about Gatsby?