I love having new people in the party... even full new parties. Most of them will be much more pleasant than the old and crusty guard. I will often leave them to discvore things on their own unless they want to know more. And I will ask someone if I see something that they are doing something oddly. I generally have access to people that are good with specific jobs and I can pool their knowledge to figure out if I can suggest something better.

I will generally ask people why they are doing something and then suggest an alteranitev. The biggest is probably fresh tanks that don't yet understand AOE threat - so the inital sugestion is spam flash if needed or use overpower a couple of times.