How does Nick describe himself at the beginning of The Great Gatsby?
Nick's description of himself in the beginning focuses on the change that has occurred because of the events in New York. He explains that he comes from a well-known working family, well-off but not extremely wealthy, and that before going to New York, he was a tolerant person to whom people told their secrets.
...after boasting this way of my tolerance, I come to the admission that it has a limit... 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.
(Fitzgerald, The Great Gatsby, mrbye.com)
The events he experienced changed him; he doesn't want to see people's secrets or attend parties, but to live in peace and quiet. He has seen the underbelly of Old Money, with their prejudices and derision for people who work for their money -- as he himself does -- and he is no longer the idealistic young man he was before. He also learns that he has no romantic notions about people and life; he refuses to see Jordan Baker again because he knows that she is not committed to an honest relationship. Essentially, his description is of a young man, just entering mental adulthood, whose innocence has been mostly shattered by the selfish people he has met.
In the very opening lines of the novel, Nick describes himself as a man that is inclined to reserve all jugdement. It was his father's advice that has made him that way. His father warned him about critizing others:
"Whenever you feel like criticizing any one,” he told me, “just remember that all the people in this world haven’t had the advantages that you’ve had.”
Consequently, Nick has been privy to many secrets, or so he says.
I’m inclined to reserve all judgments, a habit that has opened up many curious natures to me and also made me the victim of not a few veteran bores.
However, Nick admits that his tolerence has a limit and says:
And, after boasting this way of my tolerance, I come to the admission that it has a limit. Conduct may be founded on the hard rock or the wet marshes, but after a certain point I don’t care what it’s founded on.
Nick then states that something has changed in him since he had returned from the East, making him no longer as tolerant as he was. So, it is safe to assume that being on the East changed him and that he was different before he went there (perhaps more naive) :
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. Only Gatsby, the man who gives his name to this book, was exempt from my reaction — Gatsby, who represented everything for which I have an unaffected scorn.
So, Nick before East was a young man with an open heart we could say, but he was restless- that is the reason why he left for East in the first place.
I participated in that delayed Teutonic migration known as the Great War. I enjoyed the counter-raid so thoroughly that I came back restless. Instead of being the warm centre of the world, the Middle West now seemed like the ragged edge of the universe— so I decided to go East and learn the bond business. Everybody I knew was in the bond business, so I supposed it could support one more single man. All my aunts and uncles talked it over as if they were choosing a prep school for me, and finally said, “Why — ye — es,” with very grave, hesitant faces. Father agreed to finance me for a year, and after various delays I came East, permanently, I thought, in the spring of twenty-two.
So, we know that Nick in the beginning of the book was an open minded youth, that enjoyed a degree of support (and presumably love) from his family. He was also eager for chance and restless.
Nick does not talk a great deal about himself in the beggining of the book (or in the middle or end for that matter).He does not give us details about his life but he says enough to make us somewhat familiar with his character. It is interesting that in the very beginning he mentions Gatsby, who has obviously had a big influence on his life and the shaping of his personality.