Just a general note, but all the tanks now have a "block" skill: short cooldown, short duration, medium-high mitigation. This is meant to be used during tank busters to mitigate the damage, and can be used by the OT on the MT for the same effect.

DRK- TBN is your buster blocker, cast it on self if MT, on MT if OT. Pretty obvious. Always keep 3k mp in the chamber for tougher fights. Not sure how well double DRK setups will work.

PLD - Sheltron is literally your block button. You also have that holy orb looking thing to cast on the MT if you are OT. Can't remember the name. Also cover, of course, but that has a lengthy cooldown that will prevent it from being useful most of the time. All PLD buster blockers are gauge dependent, so keep 50 on hand during hard fights.

Gunbreaker - Heart of Stone. Cast on yourself, cast on the MT, same button, blocks 15%. Easiest use skill. No gauge or currency to worry about. Can also use your regen on the MT if things are bad enough.

War - Raw intuition is your block as MT, but as OT you are meant to use Nascent flash on the MT and very likely bust off some gauge nukes to maximize the healing potential. This is more a clean up rather than a mitigation, but it's all they have while OT. Would recommend saving up one charge of infuriate at all times during the worst fights so you can use that to heal the MT.

And the reason I'm posting this now is I get the feeling raids are gonna be /really/ harsh if you mess this up...