In Final Fantasy XIV, high in HP and trained in defense, a tank serves as the party's shield. Skilled at keeping a foe's attention and bearing the brunt of enemy attacks. I'm writing this guide in hopes to try to help new players acclimate to tanking in FFXIV.
Tanking in the world of Final Fantasy XIV is rewarding and really easy, however, many people shy away from it because there is a stigma that it can be overwhelming. here is a video help teach you about the different tanks, and help introduce you to some starting tips and tricks to help make you a great tank.
Generally speaking, mitigating tankbusters takes priority over mitigating auto-attacks and unavoidable AoE damage simply because most tankbusters will outright kill you if you don't mitigate them. But that isn't to say you shouldn't mitigate autos and raidwides, they can be just as dangerous and know one knows this better than your healers. Communicate with them to find out where areas of high pressure are and try to have a cooldown to cover those areas.
Some general tips:
Plan out your cooldown usage.
Nothing should be reactionary at this level of play. Nor should anything be held onto in case of an emergency. It helps to look up the timeline of a given fight to see where the damage happens. I personally make a spreadsheet for each fight and share it with my team so we can coordinate mitigation tools.
It's common for new tanks to treat their invulnerability cooldown as a panic button.
Don't do that. Invulns are especially good for soaking heavy tankbusters since they free up your damage reduction cooldowns to be used elsewhere.
Try to find places to squeeze in extra cooldown uses.
If, for example, you find that you don't use Rampart until about two minutes into a fight, try to find a spot to use it within the first 30s. Since it has a 90s recast, it will be back up in time for when you need it, and mitigating some damage is always better than mitigating no damage.
Consider the durations of your cooldowns.
It's often possible to mitigate multiple sources of damage with a single cooldown. For instance, if a boss uses a raidwide and then follows up with a tankbuster five seconds later, popping your cooldown for the buster in advance allows you to also mitigate that raidwide.
Learn to differentiate between physical damage and magical damage.
This is especially important as a Dark Knight since Dark Mind can only be used to mitigate magical damage.
Your party has mitigation tools too, don't be afraid to ask for them.
Reprisal, Dismantle, Addle, and Feint are usually used to mitigate raidwide damage, but they can be used for tankbusters as well. And they're all on relatively short cooldowns. Ranged DPS can also give you Palisade and Apocatastasis which reduce physical and magical damage respectively by 20% for 10s.
Don't think only in terms of "main tank" and "off-tank".
Your party has access to two tanks-worth of cooldowns, try to make use of both sets. It is sometimes better to swap even when you aren't forced to simply to gain access to a fresh set of cooldowns, or to have the other tank use their invuln on an upcoming buster.
Tank stance is extremely useful for when you're learning a fight, but you should try to phase it out as you come to learn where you take damage and how you'll mitigate it. It can also be helpful in emergencies, like when a player dies and the healers need to recover.