As a curmudgeon who survived Usenet, People Connection, MySpace, and Yahoo Groups (and who is waiting for the current generation of online communities to implode like their predecessors) I have one piece of advice for authors engaging publicly--be it on social media or IRL:
Don't be a dick.
It's a simple thing, but seemingly hard for a lot of folks to grok. Don't worry, not being a dick doesn't equate to being a doormat. You can be firm in your convictions without making shit personal. It's also okay to ignore the misanthropes. Some comments shouldn't be acknowledged, much like some people aren't worth your time. Some of the worst offenders aren't even people, they're bots.
On the internet where things never die, take the high road and don't be a dick.