Tanking question

[Aluja89]

If I level a Dragoon from 1-70 and then pick up Sage, am I supposed to know how to heal effectively right away?

This isn't a player problem, it's a game design problem. It allows players to pick up new roles and jobs at a higher level without having to go through the learning experience to get there.

If you're going straight into group content, yes.

Also, you don't need firsthand experience if people stopped staring at their hotbars they could learn a thing or two from looking at others, but that's wishful thinking I suppose.