Montresor carefully plans his revenge against Fortunato:

He ensures that his servants are out of the house the night of the murder so that nobody can report that Fortunato was in his house the night he disappeared.

He picks the night of the Carnival, a raucous evening of partying, when Fortunato's disappearance is unlikely to be noticed.

He ensures that Fortunato is drunk so that he won't be alert to danger. Montresor even takes liquor with him into the catacombs to keep Fortunato from sobering up.

He also never lets on that he is angry at Fortunato, so Fortunato has no reason to suspect he will be murdered. 

Finally, he plans to commit his murder in isolated catacombs where nobody will hear Fortunato's cries for help. 

Montresor's goals are twofold: first, he wants Fortunato to know that he is taking vengeance on him, and second, he wants to be sure nobody else discovers the murder. Because he chains and then walls up Fortunato, Fortunato clearly understands that what is happening is no accident. Further, because Montresor is telling the story 50 years after the fact, most likely as a deathbed confession, we know that he got away with his crime. 

Montresor has his plan carefully worked out. First, he makes sure his servants will be out of the house by telling them he will be out all night, but he wants them to stay at home and not go to Carnivale. Montresor knows the servants will leave. This way, no one will see Fortunato go to Montresor's house. Next, Montresor uses Fortunato's ego against him by saying he needs Fortunato's expert opinion on some wine he has bought. Then Montresor baits Fortunato by saying he'll get Luchesi, another wine expert, to do it. Of course, Fortunato takes the bait and insists on going with Montresor. Montresor is very nice to Fortunato beforehand so Fortunato will have no reason to think that anything is wrong. Once in the catacombs, Montresor encourages Fortunato to drink more so it will be easier to chain him to the wall. Montresor then walls Fortunato in the alcove so he will never be found. Montresor is telling the story fifty years after the crime, so he is never caught and does committ the perfect crime, as far as carrying out the murder.

Montresor's first step in his revenge plot is to appear amicable toward Fortunato during their interactions to quell his suspicions and gain his trust. Montresor also specifically chooses to approach Fortunato during the carnival season, which is a chaotic time when Fortunato is more than likely intoxicated. Montresor then fabricates a story regarding a rare pipe of Amontillado because he is aware of Fortunato's obsession with wine. He is also aware that Fortunato is extremely prideful, which is why he mentions Luchresi's name.

Before Montresor invites Fortunato to his palazzo, he makes sure to inform his servants that he will not return home until the following morning. Montresor understands that his servants will immediately abandon their duties later that night, leaving the house empty. Montresor then leads Fortunato deep into his vaults and continually offers him wine as they journey to the back of the catacombs. By continually offering Fortunato wine, Montresor further impairs Fortunato's judgment, which makes it significantly easier to shackle him to the back wall. Montresor also had the forethought to carry a trowel with him into the vaults in order to construct a wall around his enemy.