Where does Winson sit to write?
In order to elude the view of the telescreen, Winston sits in a particular corner of his apartment that by some stroke of luck is actually invisible to the telescreen because of its placement. Winston believes that the alcove was originally supposed to hold bookshelves but since they were absent, there was a small space that the telescreen could not cover because of it being placed not in the opposite wall but on the "long wall" near the window.
It is vital that Winston hides the activity of writing as it will be seen as extremely suspicious by "Big Brother" who may or may not be watching through the telescreen. In fact, Winston assumes that he is always watching as that is the safer way to approach life in Oceania.