Pause before you share.

When you feel strong emotions - happiness, anger, pride, vindication, - and that emotions pushes you to share a "fact" with others STOP. Above all, it's these things that you must fact-check.

Why? Because you're already likely to check things you know are important to get right, and you're predisposed to analyze things that put you an intellectual frame of mind. But things that make you angry or overjoyed, well...our record as humans are not good with these things.