When confronted with a lie, it's not enough to simply lay out the facts. It would make sense to simply lay out the truth and figure your work is done. It's not.
President Barack Obama found this out the hard way.
It's a lie that Barack Obama wasn't born in the United States and is therefore ineligible to be president. This isn't a partisan issue. Mainstream Republicans say it's not a real controversy.
Obama was born in Hawaii; that is a fact, and when he was running for president, his campaign tried to combat this lie by (a) letting the press report the truth and (b) giving out copies of his birth records and the birth announcements from newspapers at the time.
Just sending out the truth didn't work, because the people who believe this lie, nicknamed "birthers," want to believe it. They discounted all evidence to the contrary. Even after the supposed smoking gun of the birthers, a birth certificate from Nigeria, turned out to be a bad forgery, that didn't kill the story.
Given a strong enough motive, people will continue to believe a lie, no matter how many facts they're exposed to or how much you undercut their supposed proof.
That's why you have to attack lies from three different directions.
1) Motive
This may be the most important counter to a lie. Chip away at the motive. Expose those who keep repeating the lie.
An effective tactic in combating the lie about Obama was to link birthers with other groups happily spreading the lie, those groups happening to be the KKK and other racist groups.
2) Facts
Only after you've attacked the motive should you start laying out the facts.
More important than the volume of evidence is the variety of evidence: photos, witnesses, documents, video.
Use independent sources and physical evidence whenever possible. That gives you more credibility. If it all comes from one source, it's easier to attack.
3) Mockery
Research shows that mockery is one of the most effective techniques for persuasion. When you provide evidence of the truth, and they counter with their own supposed evidence, it can make it look like a legitimate debate.
Average people who don't have the time to research who's right and who's wrong may just throw up their hands, which is sometimes the whole point of a lie.
In the Obama example, the birthers wrapped themselves in the Constitution and patriotism, complicating any attack their motives. The most effective attack against them wasn't to talk about the evidence, about birth certificates and forgery and facts. The best attack was to mock them, to lump birthers in with crackpots who still believe the earth was flat and conspiracy theorists who think the NASA faked the moon landing.