Oceania is a technologically backwards society. Quality of life and literacy are kept deliberately low to make it easier to maintain power. In the 1980's they use mostly technology developed in the 30's-50's They rely on pneumatic message tubes within the Ministries. Any phone calls are by landline, long distance is by radio (which are not cleared for civilian use). Their complicated information control and suppression works mainly on human brainpower, committees, and paper records. Technological development is stagnant, except for warfare and espionage, and even then not much better. The highlights of their technology include the speakwrite, which directly transfers dictated words to paper, various mechanical algorithms for assembling formulaic songs and novellas for the ignorant masses (eliminating the need for creative artists), and of course the telescreen.
The telescreen acts simultaneously as a television, a camera, and a microphone. Only members of the Inner party can turn theirs off, while everyone else can only dim them, and while on they constantly transmit their surveillance to the Party (via landline - broadcast TV would be vulnerable to picking up rogue signals). They constantly cycle through the feed of every telescreen, scrutinizing everyone within view intently. They can't see every screen at once, but they could potentially be watching any screen at any time. Every Party member has a Telescreen in his or her home, and anything he or she does at home will probably be seen (except after lights out, though sounds will still be heard). Most proles don't have screens in their homes, and the party relies on patrols more to keep an eye in the prole neighborhoods, but there are still screens posted on some streets. Also, there are mics hidden about the countryside. They're sparse but one must still be careful (probably concentrated around trails used for Community Hikes).
For the Inner Party, the most important thing to remember is that Big Brother is Watching You. Inner Party members wear the distinctive uniform of a blue jumpsuit and are expected to conform to the utmost, so doing anything but undercover intel/sabotage work would be next to impossible for an Assassin amongst them. Eccentricities or deviations from routine are all highly dangerous. The Proles are considered beneath suspicion, the ignorant-est and unwashed masses, so as long as they don't do anything too outlandish, a Prole won't attract too much notice in a crowd. If someone could get on the rooftops stealthily, they should be safe from all surveillance except helicopter sweeps.
Common criminals are sent to forced labor camps, Thought Criminals (always Party members) are made into Unpersons. An unperson is tortured into confessing all kinds of crimes against the state, exterminated, and then erased from all records. Often times they are brainwashed into being completely repentant of their unorthodoxy and loving Big Brother first, to eliminate any chance of martyrdom.