First of all, it helps to have a basic knowledge of music and rhythm to ad-lib, and/or improvise. Ad-libbing is, basically, “playing around with the tune”, using licks, riffs and scales (and/or whatever comes to mind) usually in a dramatic or emotional part of a song.
how to breathe properly
Learning to breathe properly is vital to a centered voice
finding the pure note
Looking for Shangri La for the pure note?
big vibratos
Vibrato (“a pulsating effect in the vocal tone produced by slight and rapid variations in pitch”)