I always say "hi" "hello" "thank you all" and even a '"take care" if people are answering. If there's a first timer in our group, I take the time to explain boss mechanics. If I'm the first timer ( most likely with my PLD), I always say I'm new to tanking/speed running this place. Sometimes, people are kind enough to say "it's ok" or "Do smaller pulls if you're not comfortable with this dungeon". When I play my SCH with a new tank, I tell them to take it easy. I apologize when I make mistakes.

I think it's important to communicate, or at least answer to others.