I'm often asked how to learn to play a smooth and reliable right hand tremolo technique. And how can my hands and fingers possibly play tremolo non stop for several minutes at a time.
These are two very good questions and here I will try to explain.
The matter of playing right hand tremolo is both quite simple but also complicated. It is simply the rapid repetition of a chosen right hand finger pattern, the most common being p-a-m-i (thumb, annular or "ring" finger, middle and index finger) with other patterns being preferred by some players. The a-m-i fingers play the melody while the thumb p plays a bass line accompaniment. The idea is to create the illusion of a continuous stream of melody notes whereas in actual fact, with the most common tremolo pattern, there is a tiny pause or break when each bass note is played by the thumb. eg. p-a-m-i-p-a-m-i-p-a-m-i-p-a-m-i-p-a-m-i. The end result is the closest the guitar can come to producing long sustained, notes such as a violinist and singer are capable of.
The process of learning tremolo technique so that it happens automatically and without pain is a long, slow, gradual one. Just how long it takes to perfect varies from person to person. It took me about a year before I could play tremolo well and several years after that to become completely confident playing it in concerts.
The positioning of the right hand is important and needs to be worked out with advice from an experienced guitar teacher. The arm, wrist and hand should be relaxed to avoid tension. Don't overdo any technical exercises and if you experience pain, please stop immediately. It's important to rest and try again later.
You must start practicing the right hand pattern quite slowly and precisely with a metronome to help ensure the notes, when played at speed, are perfectly in time as they have to be. Many players who are impatient and hurry can end up with an uneven or 'galloping' tremolo. Each finger should strike the string with the same amount of weight as the others and that comes with careful training.
If you are already a reasonably experienced guitarist, then you should be able to decide which notes to play when practicing but don't try to play a whole piece of music yet. You could just play the a-m-i fingers on the open E string and the thumb on open D. This can become boring after a while, so you might like to change the notes. But remember that the point while learning the tremolo technique is to have minimal effort for the left hand and maximum focus on the right hand. Note that Estudio Sencillo 3 (Simple Study 3) by Leo Brouwer is quite useful as it can be adapted as a short tremolo piece just by repeating the melody notes. You will find there are other examples and studies written for the purpose of practicing tremolo.
It is also important that you train your fingers so that they become used to playing the a-m-i pattern on different strings, not just the first (E) string. Some guitarists are instructed to start their tremolo exercises on the second (B) string which requires more control because you have to avoid also hitting the first string.
As you become used to the chosen slow tempo, try increasing the metronome setting by a notch or two at a time. Gradually increase the tempo to the point where your fingers cannot cope, then ease back a notch or two where it becomes easy again.
You can also try, at a slow tempo, playing the tremolo (a-m-i) with rest stroke (apoyando) instead of free stroke (tirando). I'm not sure why this helps but it seems a way of emphasizing the finger movement but it also helps add variety to your practice. Monotony and boredom are to be avoided!
Another useful exercise to help train the right hand fingers is to change the tremolo rhythm. Instead of even notes, try playing with a dotted rhythm. Again try it first with a slow tempo. You will find that because of the dotted rhythm, some of the finger exchanges will be faster than usual.
It is also important to consider the movement of the thumb. When the fingers are playing the repeated a-m-i pattern, the thumb often has to move between notes on different strings as you can see if you read the Recuerdos del la Alhambra sheet music. This is why in tremolo exercises it is helpful and important to train the thumb to play on different strings. For example, while playing a-m-i on the first string, you could use the thumb to play each of the open bass strings E-A-D or E-D-A. Sometimes too, the thumb might also be needed to play notes on the second and third strings.
Of course, there is much more to the story and other players will have different ideas and opinions on the subject. These are just mine based on my experience.
Watch this space for further tips on tremolo.