For Edgar Allan Poe's "The House of Usher," you will have more than enough for three paragraphs if you review the story, noting the parallels between the house and the family. For an opening, you can certainly draw upon the double entendre of the title: the house as the mansion and the house as the family [the narrator alludes to this in paragraph 3]. For, both the mansion and the family are of aristocratic stature, they have been around a long time, and they are both isolated and fast becoming victimized by their internal decay.
With these three conditions in which the family and the mansion are parallel, you can easily construct the body of your essay, locating supporting details in the narrative. For instance, in the exposition of the story, the description of the "mansion of gloom" is much like that of one that follows of Madeline as the narrator shudders upon gazing at the
inverted images of the gray sedge, and the ghastly tree stems, and the vacant and eyelike windows
In fact, the atmosphere of the mansion seems connected with the underworld and with decay and disease (par.4) Later in the narrative, the life of Roderick is, indeed, connected with the subterranean regions of the house and the decay and disease of his sister.
These parallels run throughout the narrative; you will have no difficulty if you return to the story and peruse with such parallels in mind. As an aid to the actual writing of your essay, see the site below that has helpful points.