Veterans: How do you pass on years of FFXIV knowledge

[Nyastra]

Admittedly surprised at the new player experience you describe - the game has a reputation for being supportive toward sprouts and, beyond some very rare encounters with arrogant elitists who think everyone is doing everything wrong, have never really experienced anything like that.

As you say though - a great deal of it is trial and error from first-hand experience.

Likewise, I too was surprised. We did Sastasha which is obviously the first dungeon in the game, and one person's reaction was instantly "Our tank is a bot" to which I had to say, no our tank is a new player. Similarly to that, Aurum Vale (golly we know, we know) our one DPS was terribly toxic the whole time based on how our tank was pulling few mobs at a time. I ended up vote kicking him when he kept trashing everyone else including me though. Maybe it's an EU thing? I don't know. My first experience with this game was based on NA servers, it's only this year that I moved to EU.

[Carin-Eri]

Likewise, I too was surprised. We did Sastasha which is obviously the first dungeon in the game, and one person's reaction was instantly "Our tank is a bot" to which I had to say, no our tank is a new player. Similarly to that, Aurum Vale (golly we know, we know) our one DPS was terribly toxic the whole time based on how our tank was pulling few mobs at a time. I ended up vote kicking him when he kept trashing everyone else including me though. Maybe it's an EU thing? I don't know. My first experience with this game was based on NA servers, it's only this year that I moved to EU.

Entirely possible that the first one was a troll? I mean, the 'Sprout' over the player's head should give some indication, as well as them stopping for cutscenes.

I guess one useful piece of advice - one that I was given when I was a Sprout - would be to have your fiancé say, in chat, "First time" (or words to that effect); that way the rest of the team know from the onset and you don't need to rely on them being attentive enough to notice by themselves.

[Exmo]

Generally, answer questions only when asked.
Offer the bare minimum of guidance unless requested.

However, do offer guidance on things like etiquette. Always say hi at the start of a duty and gg at the end. Tell people when it's your first time so they'll be more lenient and patient.
Advise on certain QoL settings like disabling the resident evil tank controls, which traps a lot of sprouts. Or how to reorganize the HUD, without it turning into a lesson on how their HUD should look according to your own preference.