What does Nick say in chapter 1 of The Great Gatsby about how his experience in the East has changed him?
Nick begins his narrative of the adventures he had in the East by reflecting on what he learned from them. He had moved East with high expectations that he would be able to build himself a great career as a Wall Street bondsman, and he looked forward to encountering new people and activities as he lived and worked in that area which was so different from the quiet conservatism of the "Middle Western city" that was his hometown.
The actual experience was not what he had expected. Nick discovered that he was not attracted to all the flamboyant activities and outlandish personalities that dominated New York society. He had moved East thinking that he was a very tolerant individual who was able to "reserve all judgments" about people around him. Once there and involved with Easterners and their ways of life, however, Nick came to realize that he could not ignore the superficiality of their lifestyle and attitude.
When I came back from the East last autumn I felt that I wanted the world to be in uniform and at a sort of moral attention forever; I wanted no more riotous excursions with privileged glimpses into the human heart.
When Nick talks about his experience in the East he is talking about everything that is about to transpire throughout the rest of the novel. This adventure has made him want to lead a moral life and one that is without unnecessary adventure and lavishness. His experiences with Gatsby have given him enough of these things. He is wanting a much quieter life now.