I spend on average about 30 minutes a day on the practice of scales. I usually aim for a speed of about 80 to 100 bpm on the metronome. I sometimes go too fast but this is a recipe for disaster. You end up losing the pulse and it simply sounds sloppy unless of course you are highly experienced in your scale playing and know what you are doing. I have made the mistake of trying to play too fast but now I start off slowly usually using rest strokes and gradually build speed after gradual repitition. I am currently working on two and three octave C and G scales both major and minor (natural, melodic and harmonic). I practise the scales using im, mi, ma, am and imam and I have also tried ia, and ai.
I also make sure that the left hand is placed in a relaxed and comfortable manner.
John Mills once said
'Scale practice must be done most of the time to a metronome; not particularly to see how fast a scale can be played, but more importantly to how fast a scale can be played, but more importantly, to give the pupil a solid rhythmic pulse which eventually will be become natural and inbuilt.'
From an article entitled Notes on Technique by John Mills
Guitar the magazine for all guitarists September 1982.
In this article he also recommends practising scales using p and i in the right hand, quote 'as this is good for passages using scales in the bass part in 16th and some 17th Century music......He goes on to say that the p and i fingering is not used much in Great Britain but that he has seen it used with great speed precision in other countries.
I am interested in getting advice from advanced players as I am currently just over half way through the grades for Classical Guitar and I am looking for tips on improving my technique and ability to play in front of a small audience.