I have no idea why, but they are the bane of my life! They should be one of the easiest techniques to master, as they are the most natural of all right hand techniques, after playing block chords. Start arpeggios by playing block chords to get your fingers used to gripping three or four strings at the same time. Practice arpeggios using tirando. What to do with your thumb whilst i-m-a are playing? My advice is only to plant the thumb whilst the finger previous to the thumb is pressing. That way, your thumb will learn maximum flexibility. If you habitually rest your thumb on a bass string, you will always be anchored, but thumb dependent, and you will lose flexibility of thumb movement. There are two kinds of arpeggios: ascending and descending and these are played in two different ways: using a block plant and using a sequential plant.
Put all your fingers down on the strings first: p-i-m-a and then apply pressure to each in turn until the string is released, go onto the next one and continue. Is is very useful to practice this very slowly and deliberately. Practice this with both ascending and descending arpeggios.
In this way of tackling arpeggios each finger is placed and pressing is done sequentially. Here you should not rest your thumb on any string!
Particularly common in flamenco is the i-m-a arpeggio that uses no thumb stroke. Practice both ascending and descending variants. Use the search function for exercises and falsetas with arpeggios. You need to be pretty confident with this technique to play any kind of flamenco – even so called traditional styles such as the Moron style. Practice this with both ascending and descending arpeggios.
For the exercises below, use any chord or series of chords that you like – but keep the fingerings very simple. Try not to keep one chord pressed for hours whilst you concentrate on your right hand – you will cause unecessary strain – in this case, better just to play with open strings. Remember that you should be concentrating on right hand position & efficiency here.
In these exercises featuring simple ascending or descending arpeggios, you play a thumbed bass note with the first treble note in the first exercises and then, on the second page, the thumb comes before the trebles.
In these exercises featuring ascending and descending arpeggios combined, you play a thumbed bass note and then the first treble note [quavers or eighth notes].