Spam Heart of Corundum as often as possible. It's very strong, the heal basically can't be wasted, and it's on a short cooldown.

I don't claim to be optimal or even close to it. But I like to use Corundum + Rampart at the start, use Reprisal after a few seconds, and use Nebula as Rampart falls off. From there I kinda just use whatever is off cooldown, two at a time (Nebula counts as two). And of course, continue to use Corundum as often as possible.

Using Superbolide is tough, cause it's not worth it until you're below half HP, and some healers don't let you get that low. If you know there's one particularly tough pull, just save it for that, and tell your healer before the pull. (Still use Heart of Corundum first, because it's so free.) If you never drop below half HP, then whatever, clearly the invuln wasn't needed.

On PLD I just use Hallowed after my first round of cooldowns, on the second wall-to-wall pull, and again on the last wall-to-wall of the dungeon. (Usually those are the most damaging, and/or people have half their stuff on cooldown for it.)

Oh and I forgot Aurora (as usual). It stacks well with anything, so you can use it at basically any time. GNB has a ton of oGCDs to weave, so I just use Aurora whenever I get a break from all that button mashing.