I think the most important thing is that you have to be yourself and do nothing by force. Post in threads where you feel good and know what you are writing about.
This is the best advice here.
You can instantly tell when someone doesn't give a shit about what they're writing, doesn't understand or has inserted themselves into a thread without digesting what it's actually about. You discard the first sentence as quickly as you read it and move on to the next post. It's immediately obvious here's no substance there at all.
And I'd be just as willing to merit a good question as a good answer. No one has to pretend to be some sort of authority on a subject to have an opinion on it and that's another faux pas that comes up all the time.