It depends on how you feel about things and the effect you have on others.

Personally, I started this game as a Warrior and up until relatively recently I didn't put much playtime into other roles at all outside a bit of leveling here and there and some grinding easy content.

As far as doing dungeons go, it's easier if you've done them as another role, so you know roughly what to expect (Though, it's not always relevant to what the Tank has to do, to say nothing of how you wouldn't know what to do as that other role anyway) so reading up about the fights and mechanics can be useful too.

Alternatively, you can just try and pick up the tactics as you go, asking others if there's anything you need to do specifically for the fights if you're unsure.

Everyone was new at one point and had to figure out the dungeons. So long as you make a reasonable effort to try and get through mechanics, you should be fine.

Most dungeons tend to be straight forward anyway, there are only a few oddball ones that have some strange mechanics that you can't pick up particularly quickly (Qarn is one of them, unfortunately) the rest of the strange mechanics tend to come from Trials (But they can for the most part be solo tanked, so you can let the other Tank in the party do the work while you DPS and learn the mechanics).

Outside of Hard mode dungeons (Which I would suggest reading up on the mechanics for, irregardless of role) the only ones that come to mind as notable in terms of mechanics for Tanks are:

Sunken Temple of Qarn
Dzemael Darkhold (First boss only)
The Aurum Vale (Second boss only)
Amdapor Keep (Second boss only. Though, it's rather easy just remember to not stand near the sides when he casts Repel )
The Lost City of Amdapor - This one has tactics that everyone needs to know, not just Tanks.
Snowcloak
Bardam's Mettle

Mostly level 50 and below dungeons to be honest...

Outside of that they're mostly just "Don't stand in the AoE circles" with maybe a "Some adds spawn" thrown in to the mix.