Big Brother manipulates minds in several ways. First, the city (or all of Eurasia?) is slathered with posters of "Big Brother" with eyes "that follow you about when you move" (3) that read " BIG BROTHER IS WATCHING YOU" (3). Thus, citizens have a constant reminder that no one is to be trusted and they are always being watched. It's like living in the immediate presence of an omniscient god, which would be intimidating and would curb your impulse to try anything that may be construed as questionable or subversive.
There are police helicopters that hover and look into people's windows intermittently, which cannot be blocked out, as well as the Thought Police (4).
The telescreen, placed in each person's house (except the proles, who are not considered to be "people"), can be dimmed but never turned off, and is not only a way to distribute nonstop propaganda to the masses, but it works both ways, allowing the Thought Police to monitor every intimate moment of every person's life. The effect was that "you had to live—did live, from habit that became instinct—in the assumption that every sound you made was overheard, and, except in darkness, every movement scrutinized" (5).
The most powerful form of manipulation was the alteration of the language--called Newspeak--to eliminate as many words as possible. Through limiting and simplifying the language, the government understands that it limits the range and complexity of thought possible, as words are the carriers of ideas.