In addition to addressing the supply of real or supposed "fake news", we should also focus on the demand. To that end, here are 6 rules to go by.
(1) Remember that if a story looks too crazy to be true, it probably (but not necessarily) is.
(2) Be extra cautious if the story supports your preconceived views. We tend not to think as critically in such cases.
(3) Look for multiple attestation. If the same story is attested in multiple sources, it strengthens (but never guarantees) its credibility.
(4) If the credibility of your source is questioned by some of your more outspoken friends, see if you can link to a source that is more widely trusted. Otherwise, you might spend more time debating the credibility of the messenger than discussing the message itself.
5) Be wary of potential "false flag social media". By this I'm referring to the possibility that there are people on social media who pose as members of groups in order to discredit or demonize these groups. (Imagine liberals masquerading as Trump voters in order to reinforce the sense that they're ignorant or bigoted, or conservatives posing as liberals in order to strengthen the impression that they're elitist or anti-religion.) They could do this through publishing provocative Tweets or Facebook posts, or creating viral memes, among other means. This scenario may seem less far-fetched if we recall that Hillary Clinton reportedly had over a million fake Twitter followers during her campaign (reality is easy to distort in cyber space). In short, I'd personally be reluctant to share any social media content that works to increase animosity towards entire groups of people, especially when the creator's identity is unknown.
(6) Be kind and patient with friends who are sharing fake news. In most cases, they aren't deliberately spreading falsehood. Gently correct them without causing them to lose face.
(7) Remember that Snopes is not the mouthpiece of God. While fact-checking sites like Snopes and Politifact perform a valuable service, they are not beyond criticism.