Wanna be a bad tank? Here's what you do:
1) Don't communicate
2) Don't mark enemies
3) Don't use Flash/Circle of Scorn
4) Don't be aware of your positioning
5) Don't cycle target/attack to monitor/hold threat on multiple enemies
6) Use Provoke on something already attacking you
7) Don't follow provoke up with a shield lob or combo'd Rage of Halone
8) Be impatient
9) Don't listen
10) Don't learn
Wanna be a good one? Do the exact opposite of that.
Just to go into a little more explanation of why you want to be doing these things:
Communicate
Communication is key when progressing through content, obviously if you're running the same content with the same people over and over, communication becomes less important as you all learn how eachother play and can anticipate what eachother will do. But with random people you just meet in the Duty Finder have no clue what to expect from you, so let them know.
Mark enemies
Marking enemies lets your party know what they should be killing. If you aren't marking them, and they are attacking something you don't want them to, then you have no right to complain when they pull off you.
Use Flash/Circle of Scorn
Flash is not good enough to hold threat on it's own, but it isn't negligible. Using Circle of Scorn/Flash after a Shield Lob with CoS being off GCD is a great way to start AoE pulls. I view Flash as an extension, it's not going to generate a substantial amount of threat, but it's enough to hold something as long as it isn't being focused or heavily AoE'd.
Be aware of your positioning
Positioning is very important, face enemies away from your group, be aware of what mobs are chained together and where they can be pulled. Pay attention to what is going on around the party, keep a look out for adds and pats that may get pulled.
Cycle target/attack to monitor/hold threat on multiple enemies
As mentioned previously, Flash is not enough to hold AoE threat if all the enemies are being attacked by AoE. You will still need to use Flash, but also rotate between your targets to monitor their threat. Fast Blade > Savage Blade > And Rage of Halone will stay combo'd when you switch targets, and using Circle of Scorn/Flash will not break their chain either. So rotate between your targets, and use a combo'd Rage of Halone on anything you're about to lose threat on. This can take a lot of focus when dealing with 3 or more enemies, but pretty fun when you get the hang of it.
Don't Use Provoke on something already attacking you
Provoke is not an instant hate button, or a set amount of enmity that will continue adding to what you have. All it does is set your enmity to highest in the group +1. Which means if you're using it on something already attacking you, you just generated 1 enmity.
Follow Provoke up with a shield lob or combo'd Rage of Halone
Mentioned above all it does is set you to the highest in the group +1, so if all you do is Provoke, and then that BRD hits it in the face, it's going right back to the BRD, you HAVE to immediately re-establish a lead in enmity, which is why having a combo'd Rage of Halone ready for this is ideal.
Be Patient
Nobody is perfect, everyone needs to learn. As many have mentioned in other threads groups naturally look to the tanks to know every encounter and pull by heart, and are very quick to point out our mistakes. Sometimes the things said are accurate, and you shouldn't take offense right away. Obviously there is a limit, but try to be understanding and patient with these people anyway, they've been waiting for you to join their queue for hours, they're just a little cranky.
Listen
If someone is trying to teach you something new, at the very least hear them out. There is more than one way do some things, and just because someone does something differently, does not mean it's worse, or the wrong way to do it. Even if you are leading your party and communicating, that goes both ways, be open to what your party is trying to tell you. If your healer can't keep up with how fast you're pulling, slow down.
Learn
We are expected to know every encounter like the back of our hands, and quite honestly, we should. It's fine to not know something, but learn from your experiences. If you run a dungeon 30 times, you should know everything about it. Being able to give a quick explanation of key mechanics before a fight is extremely helpful for anyone who may have never been there before.
More things you want to do if you wanna be a bad PLD:
11) Use Rage of Halone. Not the Rage of Halone *combo*. Just Rage of Halone.
(The difference in enmity generated between a combo'd Rage of Halone and not is IMMENSE! Rage of Halone generates enmity equal to damage dealt times 10 (in shield oath). Which means hitting just Rage of Halone for like 79 damage will generate 790 enmity. Hitting them for 300 with a combo'd one will generate 3000. This is assuming shield Oath doubles your multiplier, if it isn't and something like 1.2-1.5, these numbers would look something like, non-combo'd generating between 474-593, and a combo'd one generating between 1800-2250.)
12) Stand in avoidable AoEs/casts
Example:
13) Don't Stun/Silence key abilities. (These change from fight to fight)