Help for a newer healer

[Gorvi]

Healing is all going to depend on your party setup and the fight or dungeon you're doing. Some tanks you'll be good to throw up a Stoneskin mid-battle, switch to Cleric Stance, and get a 2-3 good Stone II's in before they're even at 75% and you need to switch back. Hell, if you have a really good tank you can even run up to a group of mobs in a dungeon under the above circumstances and throw out 2-3 Holys.

That's not all cases, though. For me, a general rule is I try to keep Stoneskin up on myself and the DPSs at all times, so long as I'm not doing it when I should be curing. It's just that much more added buffer if they eat an AOE or can't/don't dodge an attack. Don't be afraid to Stoneskin a tank mid-battle even if you don't plan on DPSing, that Stoneskin on a tank with 8k HP will give you a buffer of nearly 1500 damage to do other things, like heal up a DPS, remove debuffs, raise someone who may have died, that kind of thing.

[Risvertasashi]

How 'deep' do you want to go?

If you want to do EX primals, second coil, basically all the "hard" content FFXIV has to offer... learn the fight patterns really well. You need to be able to anticipate stuff happening and already be in motion or casting. Although out-of-game guides can help, a lot you'll only learn by doing.

As a practical matter, try solo healing some EX primals (say, titan and leviathan? Or to start off a bit easier, just garuda...). When you get that down, you're doing very well.

If you're just intending to play more casually... well. Make sure to avoid oneshot mechanics and such but pretty much just heal as the damage comes. Stoneskin on DPS and other healers during downtime. Regen on the tank or anyone tanking if you can spare the GCD. If you made it through Aurum Vale leveling up, you should be fine in any level 50 dungeon as long as you're geared for it. HM primals take a bit more dodging but they're still pretty easy.