How to inprove voice quality?

Vocal hygeine. 1) limit caffeine 2) drink plenty of fluids 3) treat any acid reflux symptoms 4) avoid vocal abuse - over use or abuse of the voice.
Hard to say. With so little relevant information it is hard to speculate why this is an issue. A basic plan might include a consult with a trained speech & language pathologist who can assess your vocal mechanism. They are often part of a rehab team or office with occupational therapists. They might then offer you a plan of vocal therapy if needed. .