A set of habits for maintaining good vocal condition: hydration, warm-up, limiting smoke and alcohol, sleep.
Drink water (not ice cold!), avoid dairy before singing, get 8 hours sleep, don't strain your voice. Warm up before every session.
Vocal cords are a muscle — they need recovery and proper nutrition. Chronic strain leads to vocal nodules.
Professional singers have 'vocal rest' — 30 minutes of silence before a show.