Elvis used vibrato in every song.  He couldn’t do those slow songs with excellent vibrato without practicing, vocalizing vibrato every day.

Vibrato takes 60% more breath to sing.

Audiences are soothed by vibrato.  Imagine you are soothing the audience while you sing vibrato.

Simple Vibrato

Same as Notes Vocalizing methods but add vibrato to the end of the vowel so it has 3 cycles or more.

Long Vibrato

Same as Notes Vocalizing methods, but hold the individual note for 8 counts.  Keep the vibrato consistent till the end.

Hard Vibrato

Hold a note using a strong vibrato, almost a wobble, for 8 counts or beats.  When mastered do the counts to 12.  Then do mezzo forte.   Then forte.  Do this throughout your vocal range when vocalizing.

Vibrato should be practiced while using a metronome (on your phone).  Your vibrato cycles count must be in sync with the beats of the metronome.