Good vibrato starts with stable sustain
If straight tone already falls, shakes, or loses breath, vibrato gets messier. Train straight tone first, then add motion.
Watch width and rate
Natural-sounding vibrato usually comes from even, moderate motion. Measuring width and rate helps reveal whether it is too fast, too wide, or inconsistent.
Place it at endings first
At first, add vibrato only in the second half of a sustained note. Once entry and release are controllable, apply it to more complex phrases.