My suggestion is that you team with a healer who knows those Stormblood dungeons and understands you might make mistakes.

When pulling big groups, you want to use ideally 3 defensive cooldowns per pull.

I can't see what your Job is, but say you're WAR. For a pull that is "medium spicy" do Rampart, Reprisal, Raw Intuition (Aka Bloodwhetting, it changes to this later). For a "very spicy" pull, do Vengeance, Arm's Length, Raw Intuition (aka Bloodwhetting). You can use Raw Intuition on basically every pull. Mix in Thrill of Battle and Reprisal whenever you can. You have more defensive cooldowns than you actually need, so if the group is struggling on damage, you will want to fall back on Thrill of Battle, Equilibrium, Raw Intuition (it comes off cooldown really fast).

If these abilities don't mean much to you, it's OK, each tank has similar mitigation. Rampart + Reprisal for medium pulls, 30% damage reduction + Arm's Length for the scarier pulls.

Mastering big pulls will teach you how to mitigate bosses effectively.