This is all great advice!

But the #1 piece of advice for citing quality sources is: actually read the thing you're citing deeply enough to be highly confident that it supports your point. If it doesn't support your point, consider whether you need to change your point. If you can't even tell for sure whether it supports your point, try switching to a secondary or tertiary source. If you're already reading a broad-audience tertiary source like Wikipedia and you can't tell if it actually supports your point, consider either expressing greater uncertainty or learning more about the topic so you can be more certain (or express uncertainty with more confidence that this is the state of human knowledge, not a personal lack of knowledge).

The biggest problem I see on Medium, and increasingly much outside of Medium, is not that quality sources aren't cited. It's that they don't really support the point that the author wants them to--usually it's not actually backwards but the author states something definitively that the article shows is a possibility, or something like that.