.. will probably make up an interesting list. Catherine Deveny writes about one: vanity is unbecoming. She doesn't use those words, of course; her opinion piece is much better written.
What about the importance of modesty? Chastity? Humility? Ambition? Obedience? Right vs. wrong? Why drinking yourself silly every week at 16 years of age is dangerous? Watch your language? Respect the elderly? Moderation? Love thy neighbor? Thou shall not commit adultery (or fornication)?
It's a long list, and these topics have fallen into disuse more in some countries than in others. But that things have gone this way should be a concern, but I suspect it is being largely ignored by parents who are in a perpetual state of adolescent/teenage rebellion (despite being in their 30s or 40s perhaps. Poor kids (the children, not the parents).