In 1984 how does the Party use instincts (or lack of instincts) to control people?
The party uses instinct in two ways, one is trying to suppress it, for example in the suppression of sexual desire, the other is trying to focus it on things outside of the party, like enemies in order to make sure that people are not thinking hard or passionately about their own problems.
If you read about the way that the party builds up hate week and their incredibly nimble propaganda system, you can see how they use people's instinct towards reaction and hatred of perceived enemies to make sure their focus is always on some hazy and impossible to perceive enemy. They cannot consider their own condition because it is a necessary part of the war against these horrible enemies. They also use propaganda films of mothers being gunned down, etc., to stir up rage and hate.
In book 3, when it is time to torture Winston, the Party has spent some time researching him. He has had a reflexive instinct to wince and freak out when the noise of a rat or pitter-pattering step of a rat creep along the floor.
The Party's torturing represetative, O'Brien, takes advantage of this to get him to change and turn on Julia. When they try to put the caged helmet on top of his head he is immediately ready to do whatever they ask him because hungry rats are ready to eat his face off.
Winston has been hard to break, but this is the moment of truly controlling him.