Vibrato? Vibrato is an important and useful expressive technique in many guitar styles as well as on other instruments. Often young guitar players sound out of tune all the time, not just because they are often out of tune or play low-quality instruments, but because they use vibrato and bending with poor control.
When a string is bent, it makes the note sharp or, in other words, slightly out of tune. Vibrato usually sounds less offensive and more musical if a player holds the actual, un-bent note at pitch momentarily before starting to ‘wobble’ it. That way the note begins in tune and the listener hears the right note made more expressive with vibrato, rather than an out-of-tune beginner-ish tone.

Diagram A shows a string bent as soon as the player hits the note. This will sound out-of-tune. This is typical of beginners and guitarists with poor control. The player’s finger is usually wobbling and shaking before they even strike the note. It is like adding a note to vibrato and nearly always sounds off-key.
Diagram B. shows a string played at pitch (unbent) before then adding vibrato. If the guitar is tuned and properly intonated, this will sound in-tune. Unless a player is deliberately aiming to be slightly off-key for some musical effect, this way of playing will sound better. This technique involves adding vibrato to a note and represents a musical choice rather than a side-effect of uncontrolled technique.
Wind players and over-enthusiastic operatic or Tiny Tim-style singers can also benefit from this advice. Pay the note in tune first, then add vibrato for expression, sustain, or projection.