In other words, how has Fitzgerald chosen to tell his story? what can we see that Nick perhaps can't?
Fitzgerald sets Nick up as a credible narrator. This is important because we see the story through his filter. There needs to be some sort of balance in the midst of some pretty dysfunctional characters. Nick doesn't have any eccentricities and seems grounded. He was educated at the Ivy School Yale and fought in WW1. Nick isn't a character who needs anything. He seems to have enough money to settle down in West Egg. For much of the novel Nick is more or less a flat character. We can see life in West Egg through him. Nick observes situations without giving judgment. This allows the reader to trust Nick as a narrator and finally a character in the novel.
