One major strategy that Homer employs in order to unify the many different places and events in the story is to break up the narrative so that a group of several books will focus on just one character's actions or the events that take place in one location. The first four books focus on Telemachus, his anger at his mother's suitors, and his journey to find out about his father; then, books five through thirteen focus on Odysseus, his travels, and his eventual return to Ithaca with the help from the Phaeacians; finally, books fourteen through twenty-four focus on Odysseus's and Telemachus's actions once they are both in Ithaca and plotting their revenge on the suitors.
Further, in the middle chunk of books that focus on Odysseus and, in part, his many travels in his efforts to return home, Homer unites the many various places and events that have occurred by having Odysseus narrate them himself. Certainly, a lot happens, and it could seem very choppy to tell, from a third-person narrative point of view for example, of his journeys to Ismarus, the land of the lotus-eaters, Cyclopes Island, Circe's house, the Underworld, Thrinacia, etc. However, having Odysseus narrate this part of the story helps to unify all of these disparate episodes.