Mood, atmosphere and tone are conveyed through a few different literary techniques. The most straightforward way is through a description of the setting. Often times, descriptions within the setting symbolize something. The first paragraph of the first page in 1984 gives substantial insight. Orwell writes, "It was a bright cold day in April, and the clocks were striking thirteen." Immediately the reader gets a sense of contradiction. April is spring, and often cloudy or rainy. But here, it is both bright and cold. Furthermore, clocks only have twelve numbers, but the clock was striking thirteen.
Tone is further conveyed when, in the same paragraph, "Winston Smith, his chin nuzzled into his breast in an effort to escape the vile wind, slipped quickly through the glass doors of Victory Mansions, though not quickly enough to prevent a swirl of gritty dust from entering along with him." Tone is the author's attitude toward a subject. Winston is walking in a hunched, protective position to protect himself from "vile wind." Notice the different attitude the reader may believe the author has if Winston was walking through a beautiful spring day against a gentle, caressing wind with his chin high eye and eyes gazing about. Make sense? Because the contradictions mesh with the harsh conditions, it is likely that the author's attitude is sorrowful or even pained. The environment does not seem ideal for its inhabitants.
Perhaps a more tangible example of the tone is expressed on page 18 of 1984. After writing private thoughts in his journal that were critical about the government, the narrator tells how Winston, "could not help feeling a twinge of panic. It was absurd, since the writing of those particular words was not more dangerous than the initial act of opening the diary; but for a moment he was tempted to tear out the spoiled pages and abandon the enterprise altogether." Winston is normal citizen, yet he cannot go home and write in a journal without feeling like he will be caught. Indeed, even the act of opening the journal with no one around indicted him. This panicky feeling demonstrates that the author's attitude towards the idea of a big government is one of caution. The more freedoms we submit to the government, the more invasive (at least in Orwell's opinion) the state becomes.
I find the tone of that very first chapter to be easily labeled as suspicious, suspect, cautious, controlling, or invading. From the beginning, our traditional values are put in conflict with what we see unfolding before us. We understand and can relate to a free society that prospers. This seems to be completely opposite.
Individuals struggle. We see this as characters cook cabbage as a singular meal, their homes are terribly dirty, and they have an uninvited visitor constantly watching. However, the great images of the mottos displayed glisten in the sun. These are great towers presented to be revered.
Orwell establishes this tone through great imagery and stark contrast to our world today. I think both of these literary phrases would help answer your question.