Long time Black Mage player here. Transpose is the early way to just keep your Astral/Umbral up all the time. As you get away from ARR levels they start building around Enochian and how to keep it up. There’s literally a spell that just procs stacks of umbral and you can use it while you run around. Only time I use ley lines is if I’m going to be standing still, and unless you have a good tank/healer combo it’s sometimes hard to be sure of that. Just keep your fire/thunder quick casts going as much as you can. Enochian gives bonus damage so it’s always gotta stay up. I think the role gets much easier late game, but I’ve been doing it a long time.