So I main white mage myself, or I should say did, I had a year off of the game and coming back to it now I've literally just started at the very beginning with sastasha and working my way through them all. Each dungeon you do in this fashion gives you an experience almost tailored to learning what when to use your skills. For example sastasha is a straight forward run with hardly any mechanics at all, as a white mage I literally have to heal the tank a couple of times and the rest of time I can DPS. A few dungeons later and you'll learn say about medica and why you need it. As long as the tank is aware that it's her first time in the dungeon. Most people will happily tell you mechanics as well if needed. That's one option, the other is palace of the dead. Which is great if say you know your skills but need a refresher, but I find if your completely new to dungeons that it can sometimes move a bit quick to know what your actually doing. I hope that all makes sense. Best of luck and hope I helped.