A key point for the structure is how Fitzgerald has played with the chronology; Nick's narrative starts in the present and then from about chapter 4 onwards he starts to integrate stories of Gatsby's past, however these are not in chronological order either! I think that this is because Fitzgerald understands that 1) the reader cannot absorb lots of information at once, 2) they will not understand/believe this information until they are interested in Gatsby and 3) it further builds the mystery surrounding his character.
Fitzgerald uses a patterning through the novel; the repetition of phrases or colors etc creates shades of meaning that when repeated the reader will recognize. These patterns thread their way throughout the story and adds richness of meaning to the novel as a whole.
This links in to the 'scenic method of narrative construction'. Many scenes within the novel are parallel to or mirrored by others, most notably the party scenes.
Also note the way in which Nick interrupts the main dialogue with supplementing information about characters and past events.
I think for form relevant things you can write about is that Nick is a narrator as well as a character, and so adds extra information to the plot and about characters. This makes it easier for the reader to understand the story.
Also, as he writes in 1st person it can be seen as similar to a diary or a story of his past that he has written or is telling others.
Structure can be that it is mostly chronological but sometimes time does shift, it depends on the chapter. It often describes the past i.e. Gatsby's past.
The structure follows the usual narrative; exposition, rising action, climax, falling action and denouement.
Chapters are often separated into different sections, based on the tension - as in when the setting or time changes it can be in a new section, often accompanied by a rise or fall in the tension. Pathetic fallacy is