Originally Posted by Miltiades
Also, quests like Heroic +4's can be quite overwhelming, with lots of elites and strong mobs. A CC skill (crowd control skill, which renders a target harmless for some time) is very useful in these situations, always make sure there's at least one member with such a skill for hard quests.
And make sure that people understand that damaging an enemy that is CC'ed will break the CC. In other words, if an enemy is stunned, you will wake it up when you hit it. This means be VERY careful with AoEs and turn off the "auto target next enemy."
I'm always surprised how often I have to say this in operations... I'd be willing to bet money that breaking CC is the most common reason for wipes.