The answer to this question depends a great deal on when Ishmael leaves the Pequod!
I think, however, that Ishmael learns a great deal from the beginning of the book. Certainly, his encounter with Queequeg at the Spouter Inn and Father Mapple's sermon at the chapel in New Bedford shape his understanding of whaling. Sharing a bed with Queequeg immediately forces Ishmael out of his comfort zone. He realizes that Queequeg's "savagery" is perhaps a requirement for a harpooneer and that the voyage he is about to take will be into a place that is morally as well as physically foreign to him.
But he also learns to confront his own prejudices and understand Queequeg's humanity. Father Mapple's sermon deals with the story of Jonah. Jonah's story is significant first because it recognizes the danger whales pose, but also because, in his attempt to flee God, Jonah realizes that no place, no matter how remote, is unknown to the Lord. The lessons are that one can never hide from God and that repentance is a virtue; these are lessons Ismael will remember when he encounters Captain Ahab.