Learning Mitigation

[Casualty]

1. Find out what ability or abilities are the "tank busters" for each encounter. These will generally be the hits that will outright kill you if not mitigated and perhaps lesser ones leaving you with a sliver of life left. You can do this organically by taking a large hit or you can watch a video/read a guide
2. Mitigate those hits with invuln abilities like Hollowed Ground or find out what cooldown or set of cooldowns allow you live through the hit.
3. Find out what the raid wide AoEs are.
4. Mitigate them with things like Reprisal, Divine Veil, and Shake it Off (sorry Dark Knights)

Also, don't forget your co-tank also has cooldowns. Outside of forced tank swap fights and specific intervals, you can plan tank swaps around cooldown usage to either trivialize some busters or at the very least reduce incoming damage. Bring Shirk!