Wait
Most propagandistic claims that go viral in the first hour are corrected within twenty-four. Waiting before sharing — even for a few hours — filters out a significant share of bad material.
Source up, not down
If a viral post is making a strong claim, find a named source. If you cannot find a named source, do not redistribute the post. "A friend on Twitter said" is not a source.
Notice your own framing buttons
Propaganda works partly by activating identity. Notice when a story makes you feel strongly aligned with one side; that is exactly the moment to slow down and apply the same checks you would apply to a story for the other side.
Correct visibly
If you redistributed something that turned out to be wrong, post the correction with the same visibility as the original. Quiet deletion is its own form of misinformation.