Doing dungeons will not help you learn to play your class anymore than doing fates will.

It's all about having a good sense of mmorpgs. So far, I've leveled 4 classes to 50, 2 of which I've leveled prely through fates. I have had no problems playing either of the 4 classes, though I'm aware that I suck horribly (at least, that's what I feel) on one of them dps wise (and that was the first class I got to 50, which I took through dungeons).

Obviously, as someone who's played several other mmorpgs, ever since FFXI. There are certain aspects common to MMORPGs that I already know and apply to the way I play FFXIV: ARR. And having played all types of roles throughout my MMORPG career (and 2 of the 3 roles in FFXIV: ARR). The basics of grouping isn't a difficult concept for me to grasp. In fact, I don't know why it's so difficult for some people to grasp, unless they're completely new to mmorpgs and games, and then they should be humble enough to realize they need to ask for help to learn.