A) Do not waste time
B) Always have enough healers and be prepared to heal yourself
C) Watch your AOE and Dots
A) TANKS: Kara can be sruprisingly long if you dont pull quickly. Moving from one pull to the next is not relaxed and is not the easier route but it solves a much bigger issue. The issue of finishing kara. If the healer has at least a hand full of mana and your health is good, pull. Dont wait for the DPS to get ready.
B) Even with 3 healers some bossfights are going to expect you (usually dps and sometimes healers) to heal yourself and deal with your own problems. During Maiden and with her holy fire this is not the case. During Moroes and with his garrotes you ARE going to be expected to help deal with the problem. Be happy if the healer throws a hot on you but don't be expectant of one.
C) I know we're all big kids now and have learned time and time again how our spells can screw up CC'ed targets. Well this is a much bigger league where having those mistakes could easily cost lives. EASILY. If you dont want to be cautious then come with a lot of extra gold to pay off your friends' repair bills.