Play some solo content (that's challenging to you - maybe an unsynced dungeon) & get used to your toolkit. That's how I learned. I got to lvl50 WHM in ARR (I'm a SCH main) but never felt comfortable until HW came & I could run challenging stuff at my own pace & learn more about the playstyle of WHM & the way it uses mana.

It's worthwhile doing that for any new jobs you learn or for any you feel even the slightest bit uncomfortable with. You can then progress onto party stuff because you'll know when & if you can DPS safely.