Writing effective cards is more of an art than a science, I've found—and seems to work best when you're the one writing the cards for yourself. A good resource for those interested in learning the craft is "How to write good prompts" by Andy Matuschak: https://andymatuschak.org/prompts/

However, he's also shown that cards can be written for a general audience with careful thought, see his & Michael Nielsen's work on http://quantum.country.

I'll be curious to see how python.cards goes!