Breathing techniques, posture, projection, resonance, intonation, tone, dynamics, vowels placement, expanding vocal range, exploring rhythm, aural training, sight reading, phrasing, performance presence, vocal effects... = healthy voice.
"I want to sing like the birds sing, not worrying about who hears or what they think." - Rumi
"Music is an act of love, that's why it's so rewarding." - Bernstein