How does the narrator lure Fortunato to his death?

One word--pride.  Fortunato has apparently slighted
Montressor (the narrator) to the point where he feels must take the ultimate revenge. 
He says there have been a "thousand injuries" which he has overlooked; but Fortunato
insulted him, an act which could not go unpunished. The plan is simple, devious, and
cruel.  Montressor will lure the offender to the catacombs at his
palazzo (the underground burial place for his dead ancestors)  and then bury him
alive.

But, this plan only works if he is able to lure
Fortunato to his vaults. Montressor is apparently a student of human nature, and he uses
his knowledge to carry out his plan.  The story takes place during Carnival, festivities
similar to Mardi Gras.  He tells his servants he will be gone until the morning but they
are NOT to leave--knowing full well they will go join the festivities once they know he
is gone.  Thus, an empty palazzo.

Next, Montressor finds
the slightly drunk Fortunato and tells him he has bought a large quantity (a full pipe)
of Amontillado.  This is unlikely, since it's the middle of Carnival, and both men
express their doubts as to the authenticity of the wine.  Montressor has studied his
victim and begins to set the trap, appealing to Fortunato's pride in being the
only true connoisseur of
wine.

Montressor invites him to come and be the judge,
which he rather reluctantly agrees to do--as he has a bit of a cold and he'd rather be
part of the festivites.  Each time Fortunato appears to hesitate or falter, Montressor
invokes the name of a rival, Luchesi, to lure him back.  When Fortunato insists on
tasting the amontillado, Montressor says, "My friend, no; I will not impose upon your
good nature.  I perceive you have an engagement.  Luchesi--"  The implication, of
course, is that Luchesi would be able to do the job just as well. Each time the name is
invoked, Fortunato is even more adamant that he be taken to the wine cellar to see for
himself.  "As for Luchesi," says Fortunato, "he cannot distinguish between Sherry and
Amontillado."

Thus it continues...all the way down to the
catacombs of the palazzo.  Montressor says Fortunato should turn back because it's damp
and he doesn't want his friend to catch pneumonia, and Fortunato says he is stronger
than that.  Pride again.  Montressor offers to save him the trouble and get Luchesi, and
Fortunato is even more adamant about going.  Even at the end, Montressor acts like a
caring friend, unwilling to have Fortunato harmed or injured in any way, while Fortunato
nearly forces his way into his own grave.

The plan was just
too easy.  It hinged on the knowledge the narrator had of Fortunato's pride and the
consistency with which he used that pride against his enemy.  Montressor's definition of
revenge is that he must not be punished for his act of avenging and the "avenger must
make himself felt as such to him who has done the wrong."  The great irony, of course,
is that Fortunato did not, even at the end, understand why Montressor would do such a
thing to him--calling into question both the insult by Fortunato and the excessive
pride of his murderer.