Great songs that have vibrato.
Elvis used vibrato in every song. He couldn’t do those slow songs with excellent vibrato without vocalizing practice.
They Remind Me Too Much of Youl by Elvis
Today Tomorrow and Forever by Elvis
Vibrato takes 60% more breath to sing. Audiences are soothed by vibrato. Imagine you are soothing the audience while you sing vibrato.
Simple Vibrato
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 (6 to 7 pulses a second [Htz]). Slower than 5 Htz is a wobble. Faster than 8 Htz is a tremelo. You can practice those too.
Everyone can do it. You must start small and practice a lot. Take a song you like with a lot of vibrato. Sing a vibrato part very very low in volume, just above a whisper. Notice how Elvis lowered the volume of his voice when he sang a vibrato part. After you are consistently singing the vibrato pulses, practice it at low volume ALL THE TIME -- when driving, when at Walmart, when at the grocery store, etc....