Conspiracy Theory Debunking
One of the worst sources of misinformation on the web are conspiracy theories. Unfortunately, many of them are espoused at high levels of government. Librarians have to be the "mythbusters" for people who get sucked into sources of those conspiracy theories - the key is to present people with reliable information from verified sources (for example in the health field: WHO and the CDC.) Another task is to educate people on their source consumption - teach them to ask themselves questions about what they're reading. (Who wrote it? Is the source reliable? Are they generally accurate? Do they have an agenda?) If people ask me for information on a subject (which generally happens in a reference interview), I direct them to sources I have pre-vetted to ensure they are reliable.
It is critical for people to understand that unreliable information usually has some kind of agenda behind it, and not a good one. But we have to have the right sources at hand to misdirect them from the erroneous info. Fact checking is our friend.
Also? If they're active on social media, warning them about false viral tweets/posts is also pretty key. Once again, it boils down to critical thinking and asking questions about sources.