One thing new players should do is check out strats for dungeons online before going into DF. Even when levelling or running AK and WP it's just right to check out the strats posted online so you know the bosses abilities, and roughly what to expect.

I did encounter someone tanking in AK with DF, he said he was new but he did not even bother to check strats online. You can't really teach a tank how to tank in AK through chat window, especially since there are a lot of players who don't read and respond to chat very quickly.

Etiquette should also extend to the newbies to learn as much as they can before even heading into the dungeon as well. Older players should of course be welcoming, but the newbies have to put the work in too.