"Before playing the following tremolo exercises, 
consider your overall technique. I often observe 
students wishing to have blazing fast and even 
sounding tremolo while their scales and arpeggios 
have not been fully studied. How can we play tremolo 
if our i-m, m-a, and a-m-i scales are lacking control? 
How can we play tremolo if simple arpeggios have not 
been brought up to speed? As with any technique, a 
fast and even tremolo is reliant on accuracy, control, 
relaxation, and a well-rounded technique overall. In all 
fairness, a student who can play their scales and 
arpeggios well (with all finger combinations) will be able 
to play tremolo with ease. That said, tremolo is a 
specific type of right hand technique so practicing 
these exercises should help organize your right hand." 
in www.thisisclassicalguitar.com

"Guitar is not a sustained instrument. In plain English, 
the note dies out very quickly once it comes out. Piano 
is the same. Then there are sustained instruments 
such as violin or flute. These instruments can truly play 
long notes as written on the scores. But a guitar 
cannot create a sustained note (unless you have an 
electric guitar with a pedal). So, probably a smart 
player at some point thought he or she could use the 
fingers repeatedly to create a mandolin-like effect while 
plucking accompaniment notes with the thumb.

Therefore, tremolo is an attempt to mimic a sustained 
instrument or a singer using a guitar.

In classical guitar, tremolo is typically played P a m i, 
which is one bass note followed by three trebles - 4 
notes in total. The flamenco tremolo is made up of 5 
notes: P i a m i. The key to developing a nice and 
even tremolo is to basically do the opposite of what 
you do for fast picado. Speed burst, which is extremely 
useful for picado speed, is detrimental to 
homogeneous tremolo. In complete opposition to the 
"twitch" approach of picado, you have to consider 
each and every tremolo note as a separate entity that 
is governed by a beat (or a fraction of a beat) on the 
metronome. Tremolo has to be practised very slowly, 
giving each note equal value." in www.atrafana.com

Reference composers using tremolo: Francisco 
T醨rega, Manuel Ponce, Mario Castelnuovo-Tedesco, 
Federico Moreno Torroba, Joaqu韓 Rodrigo, Alexandre 
Tansman, and Agust韓 Barrios.