Returning player in need of advice please

[Erendis]

The best is to start healing at low level dungeons, then you can adjust slowly. It gets more difficult later. For me, the easiests dungeon to heal are Tam-Tara or Copperbell Mines, so you could try those. Actually, a lot depends on party members (some constantly get in aoe or stand in poison >.<). If you really are afraid to go into dungeons first, try out guildhests. They are short and start at level 10 and first few are really easy to heal (and you get exp bonus for doing each first time with every class).

[Garlyle]

The best is to start healing at low level dungeons, then you can adjust slowly..

Yup. NOW is the time to start getting into dungeons and learning. Sastasha, Tam-Tara Deepcroft, Copperbell Mines, and most Hests (most!) frankly deal almost no damage (they can seriously be run with 0 issue without an actual tank), so the pressure's extremely low on you. You can get used to hotkeys for targetting/casting as a result, or whatever system you so desire. Ifrit, Halatali, and Toto-Rak are a 'mid tier' where you'll be a lot more active, but still shouldn't have a lot of pressure unless your team is really bad and taking craploads of damage. Haukke onwards will be starting to challenge you if you're new to healing (though they're nowhere near unreasonable), so you want the practice while you can get it!