I've had experience tanking from TERA & I've personally been interested in tanking in FFXIV. And if there's one thing I can say from my experience tanking in FFXIV, it would be the following:
-Really KNOW your skills & what you can do with them in a given situation.
-Get comfortable with marking targets. It'll make the run a whole lot smoother.
-Don't be afraid to put your foot down & let people know that their healing or DPS output is pulling too much enmity away from you, the tank.
-You're a TANK. You have to stare danger in the face on a daily basis. You have to commit to your role & do what you need to do to make sure the run goes as smoothly as possible with minimal deaths (hopefully none) within your party.
But, of course, all of this is for naught if you don't remember the most important thing of all:
Just have fun.
If tanking isn't your thing, don't keep doing it.
I wish you luck in your future endeavors!