I say this with all seriousness. Get. Good. No really, do what every dps does and practice. Practice. Practice. You won't get good at anything unless you try and learn and improve over time. I'm not a particularly confident healer but not because they're more punishing or difficult than being a blm or drg in a movement-heavy fight, but because I don't play them enough to get comfortable and memorize my buttons and abilities. That will only come with time and effort as with literally any skill.
If you want to be a good blm, do what all the other good blms do: practice.
