How does Poe use personification in "The Fall of the House of Usher"?

This is a very interesting question, because "Fall of the House of Usher" is very much a story shaped by its use of description, and its creation of atmosphere. In this sense, Poe certainly does use personification in its usual sense, as a form of descriptive language. Early on, he describes the house's windows as "eye-like." Additionally, it's worth discussing the storm at the story's end, which is described possessing "impetuous fury" and "wrath." But even beyond this, Poe's entire story is steeped in a second level of personification, seen in his treatment of the house.
As said before, personification usually exists as a kind of descriptive language (see the examples given above), but in this particular story, the house itself exhibits a kind of personality. It is not simply the setting of the story, the house actually emerges as a character within it. It is described as having a deeply oppressive atmosphere about it, to such an effect that Roderick himself believes that the house has some kind of animating force of its own. It's interesting, then, that Poe refers to Roderick Usher as "the master of the House of Usher," when, in many respects, the house exerts such an effect upon him, that one can easily cast that relationship as the other way around.

Edgar Allan Poe uses personification in "The Fall of the House of Usher," giving human qualities to the house itself, in order to connect it to Madeline and Roderick Usher, almost as though it is also a member of the family.
The title of the story itself introduces this double meaning: the "House of Usher" is both the physical structure in which the siblings live (a dilapidated, Gothic mansion) and the family itself, symbolized by its last name. As the story begins, our narrator approaches the house. He immediately feels unsettled and uses an apt example of personification to describe the windows:

I reined my horse to the precipitous brink of a black and lurid tarn that lay in unruffled lustre by the dwelling, and gazed down -- but with a shudder even more thrilling than before -- upon the remodelled and inverted images of the gray sedge, and the ghastly tree-stems, and the vacant and eye-like windows.

Those "vacant and eye-like windows" suggest both the emptiness of the house and its impending demise ("the fall"), as well as the eerie feeling that something is watching the narrator. Though most of the story's effect comes from Poe's wealth of vivid sensory detail, an example of personification like the one above (repeated twice in the first paragraph of the story) establishes the similarity between the house and its inhabitants. Fittingly, both the building and the family collapse at the end of the story, as all three crumble and die together.