Nieman watch dog carries a summary of some research. The quote here is a summary of conclusions we might use.
Journalists should avoid presenting both sides of a story when one is false – and take into account how readers’ brains process the disagreements. The following four rules can guide their efforts.
1. State the facts without reinforcing the falsehood
2. Tell the truth with images
3. Provide a compelling storyline or mental framework for the truth
4. Discredit the source
This is one reason that propagandists can be effective simply by creating confusion. Unscrupulous campaign strategists know that if their message is initially memorable, its impression will persist long after it is debunked. (See source amnesia and emotional selection)