The trick is not to suppress a story, like you would with less sophisticated propaganda, but to frame it in a particular way. You can spin negative stories in a way that they either become tedious to the public quickly or by focussing on more or less irrelevant details and statements of officials about the story. There are probably a multitude of other tricks and techniques that are well known in the public relations industry and by now huge offices with many smart people whose sole job it is to direct a story in a particular way.