Montresor spends his energy primarily manipulating Fortunato.
First, when Montresor meets Fortunato, knowing that the other man loves fine wines, he hooks the other man's interest by saying that he has bought a rare cask (container) of amontillado. He appeals to Fortunato superior skills as a connoisseur to accompany him so that Fortunato can tell Montresor whether he has been tricked in the transaction.
The second way Montresor manipulates Fortunato is by pretending that he is willing to ask Luchesi (another connoisseur of fine wines) to check the amontillado if Fortunato is too busy. Fortunato's ego will not allow him to consider letting Montresor share the wine with anyone else, and so he insists upon going with Montresor.
A third way Montresor manipulates Fortunato is by repeatedly asking after his health as they move deeper into the catacombs beneath Montresor's palazzo. Montresor acts concerned and asks many times if Fortunato will not return above ground for the sake of his health, but he also gives Fortunato more to drink. Under these circumstances, and the repeated references to the amontillado, Fortunato refuses to leave.
In these ways, Montresor convinces Fortunato to willingly proceed to his own death.