Hate Week is another one of the methods used by the Party to direct the people's feelings of anger, frustration, and hatred towards a common enemy - in this case initially their warring enemy of Eurasia.
"The new tune which was to be the theme-song of Hate Week (the Hate Song it was called) had already been composed...." (p.155). Music can be a very powerful medium to convey ideas and spark emotions, and the Party is using a theme song to rally the people of Airstrip One.
"Squads of volunteers... were preparing the streets for Hate Week, stitching banners, painting posters, erecting flagstaffs on the roofs..." (p. 155). Visual imagery is being used by the Party to enforce the significance of the event and to further swamp the senses of the populace. It is all about making Hate Week impossible to ignore.
"As though to harmonise with the general mood, the rocket bombs had been killing larger numbers of people than usual" (p.156). The reader may infer that the Party is actually behind the bombings rather than Eurasia. The Party would inflict such suffering on its own people for the sake of creating fear and anxiety which inevitably leads to anger, hatred and violence againt a perceived enemy.
Hate Week in general would have the effect of directing people's focus of their hardships and suffering in daily life onto a common enemy (who is largely unseen). This is of course to the Party's advantage.