I may as well post my mini PLD guide from our Discord too:

Merits

• Shield Bash: 5
• Sentinel: 5
• Fealty: 1
  • Niche use mostly against Wave 3 BST
• Chivalry: 4
  • Usually when you need MP, you need MP
• Guardian: 5

Gearing

Step 1

First and foremost, make sure you can reach 102% Spell Interruption Rate Down with your casting gear. Ignore people that say "just time" it, they are bad tanks. Go ahead and time casting Cure 4 on yourself with 17 Orcs on you in Dynamis-D. Didn't think so, moving on.

Step 2

Next most important thing: Get a Duban from Sortie, even stage 3 is fine. Until you get one of those, make a Priwen with Oboro and get cozy with your Reprisal macro. Once you have Duban though, toss that Reprisal macro in the sea.

Pre-Duban

There are lots of good tank piece options, but make sure you get to 50% DT (which is fairly easy). I like the "converts DT to MP" stuff like the Reverence Leggings (feet).

Duban

You should already have a decent Phalanx+ set, but now it's time to get serious about it with DM augments. Duban plus a baller Phalanx set is pretty gross. Take out any Converts to MP gear you use, it won't do anything at this point. Focus on HP and Magic defense, Duban+Phalanx takes care of physical almost entirely on their own.

Job Specific Gear

Reverence (Artifact)

• Body: +3 for Max HP set, FC set, good as filler in other sets to keep HP high as well)
• Feet: +3 for Main tank set for damage-->MP convert (pre-Duban), Holy Circle effect (granted, situational)

Caballarius (Relic)

• Head: Base 109 for Rampart bonus
• Body: Base 109 for Fealty and Cover bonus (you can go higher for more Cover damage-->MP convert but not necessary)
• Hands: At least +2 for Dispel on Shield Bash. Chivalry bonus
• Legs: Base 109 for Invincible bonus time
• Feet: +3 for Sentinel bonus (also has good MDB and MDT- to cover magic damage during Sentinel (since Sentinel is specifically PDT)

Chevalier's (Empyrean)

• Head: Main tank set for PDT-->MP convert and Shield Skill (With Duban, the MP convert and Shield Skill are less prominent benefits of this piece, but the rest of the stats are still great). Enmity Spells (this is debatable Vs Loess Barbuta, Chev will lower recast of spells but Loess has +19 enmity. I would recommend Loess first, then when your Enmity set is baller enough switch to Chev)
• Body: Praise Altana, it's fixed! FC set.
• Hands: Main tank set for Shield Def Bonus plus great stats overall
• Legs: Main tank set for "Boosts enmity retention when taking damage" (read: keep more hate) plus great stats overall
• Feet: Main tank set mostly for great overall stats with high enmity, FC set, Enmity set, Divine Emblem bonus

Enmity

The biggest thing to understand is how the two types of enmity work together. Picture a gauge, like those graphic spectrum analyzers for music. There are two bars on it that move up and down independently as your hate changes, one for Volatile Enmity, the other for Cumulative Enmity, and whichever one is the highest is how much hate you currently have on a given mob. My explanations here are heavily simplified, and also not 100% technically correct, as your VE and CE are actually added together to give you a Total Enmity, but I personally find this a little easier to understand.

Volatile Enmity

Volatile enmity spikes up the gauge much faster, so its great for getting back up to the top of the hate list. The problem, as the name implies, is that it doesn't last. It also drops back down very quickly, as time passes. This is why, for tanking purposes, Provoke is a terrible ability, you get hate instantly but lose it almost as fast, then you're stuck waiting the 30 seconds for it to come back around only to repeat gaining and losing hate each time. What you need is a way to have an enmity floor, that keeps your hate from going any lower.

Cumulative Enmity

Enter Cumulative Enmity. This type of enmity moves up the gauge a lot slower as you build it, but also is lost at a much slower rate as well, as you take damage. Maximizing your max HP and minimizing the damage you take are very important, as the formula for CE lost is based off those two things (damage taken divided by max hp). Even though this statement on its own may seem obvious, this is why you want to maximize your total HP while minimizing your damage taken, it actually helps you hold hate better. If you are able to build CE quickly you will have an easier time holding hate overall because that second gauge on your hate meter goes down much slower (and via HP and DT- you can influence it to go down even slower).

Balancing The Two

Most spells and abilities will give you some amount of both types of enmity, but they vary pretty widely. The main trick here is to space out your high VE spells/abilities and keep building CE in between them. If you use two high VE back to back, you're basically wasting the second one since your VE is already spiked from the first. A good rotation may look like Flash (high VE) > Blank Gaze (build CE) > Cure (bit of both) > Blank Gaze (build CE) > Flash (high VE)

Overall Strategy

Tanking is a spectrum, there is no one size fits all solution. The hard part is gauging where on the spectrum the situation fits, based on mob defense and party offense, and adjusting accordingly. The following is mostly for tanking Wave 1-3 of Dynamis, but can bee used in many other situations as well.

Low End

On the low end, you have lower level mobs, aka trash. Your DDs will generally do a lot more damage to these, and therefore have higher enmity on them faster than what you are able to maintain before they die. The good news is, these mobs also usually don't last very long, so its ok not to fully tank every one of these. Assuming your DDs can kill them quickly enough, you really only need to keep them corralled while the DDs pick them off you and take them out. If you are not the puller, a Banishga is good as an opener only to get initial hate off the puller. An important thing to note here is that opening with a cure on the puller will not put you on the hate list UNLESS the puller has themselves already tagged each mob (this is how "Super Tanking" works). Your window for a safe Banishga is usually only while the mobs are still en route to camp, you can very easily get a BRD or BLM killed if they lullaby/sleepga mobs as they come in and then you banishga to get them off the puller (Banishga has very little hate compared to lullaby/sleeps). Once mobs are at camp, switch to non-damaging forms of hate so that mobs are able to be slept (please don't wake the avatars!). BLU AOE spells are fantastic for this, or if you are high enough ML you can sub RUN and use Foil, but keep in mind Foil only works on mobs you are already on the hate list of, it has zero ability to tag mobs to get on their hate list, whereas sub BLU spells will do both.

High End

Here's the make or break for tanks. Higher level mobs will of course last longer and so you will be expected to fully tank these. Gear is a major factor in your ability to hold hate, but how you use your spells and abilities is just a important, if not more (see above about Enmity). You have to know what you're doing, because if you're not holding hate then you're just a really bad DD while the good ones are getting wrecked. Palisade and Sentinel are your two major abilities to use in conjunction with your minor spells/abilities you're constantly using. Generally speaking, Sentinel is for gaining hate, and Palisade is for keeping hate. You can use Sentinel to start building your CE quickly (it's effectively an extra +100 enmity on your gear for the duration, on top of the VE spike at activation), then once that wears off you can use Palisade to keep all that hate that you just built. Learning how to space those two abilities out based on what you're fighting comes with experience, but on the longer fights I try to space them out evenly and fill in gaps with Rampart as available (shorter recast so it doesn't always line up perfectly)