In the first few chapters of The Great Gatsby by F. Scott Fitzgerald, what is the most important mood and what techniques have been used to create...

The mood in the first few chapters is somewhat sad.  Nick Carraway, the narrator, is telling the story after all the events have taken place, and he uses foreshadowing to help establish this mood.  He says, in part, "Gatsby turned out all right at the end; it is what preyed on Gatsby, what foul dust floated in the wake of his dreams that temporarily closed out my interest in the abortive sorrows and short-winded elations of men."  Such a statement lets us know that someone good comes to harm, that something tragic is going to occur, and that the events will be so disillusioning that they will cause this young man to want to withdraw from the world.  As a result of this foreshadowing of tragedy, the mood could also be described as foreboding.  There is a sense of something coming.  Nick says that he "came back [from the war feeling] restless," and his restlessness affects the mood as we await whatever tragedy we know to be inevitable.