Only mentioning informations that suit the mainstream narrative while hiding anything that doesn't.
It is possible to promote a completely false narrative even without ever resorting to false information, by just relying on partial or incomplete truths: because for the average mind what is not mentioned does not exist, by continuously reporting facts/informations/arguments that confirm the mainstream narrative while at the same time systematically ignoring all those that do the opposite, mass media are able to create a distorted or even completely inverted narrative even without the need of lies.
One of the main advantages of this tactic is precisely that their employers cannot be accused of being liars, mantaining an air of honesty.