Flash

[Skull_Angel]

ive started using this rule on flash.
if its an AOE heavy party i do the following:
(Flash x Number of Mobs) +1. So if there are 3 mobs, i Flash 4 times. this seems to hold adequate threat during the initial AOE-fest. then i start working on my rotations, throwing in a flash every rotation or so to keep threat on additional mobs.

I've used this rule for helping people learning to tank since somewhere around 1.23 and it's great advice for people just starting out in most instances. Once you have a good feel for AoE threat generation, you can expand upon it with rotating different abilities after the initial AoE threat snap [situational].