While I have a laundry list of things I'd like to change with this game's UX, the one that I think would make the biggest difference remains something not strictly UI: consolidate all the initial Active Help entries into one "Getting Started" entry.

At least last time I checked, when you start a new character the Active Help will pop up to tell you how you can move, that icons over an NPC's head denote types of interactions, that you can click on (or select and press the Interact button) those NPCs to accept or turn in quests, etc. Almost everyone who has ever played an MMO—or really, most video games—will almost immediately turn off the Active Help system as a result... which means when there are things unique to FFXIV (or to the job you're leveling) later, you've already turned off the system and so do not get those tips.

Now, it's been a while since I started a fresh character, so they may have changed it. But if it still functions that way, I remain of the opinion that it would be one of the smallest changes you could make with one of the biggest impacts.