Hand frame
Set up the hand frame from the 3rd and 4th fingers with the 1st and low 2nd fingers stretching back. Practice backward stretch exercises where the 1st finger leads coming down and the rest of the hand follows. Building 10ths from the octave position by stretching the 1st finger back is also useful.
Lift and fall from the base knuckle
Finger action involves muscles and tendons that connect much further back into the arm than the base joint of the finger, but it is useful to focus on this joint to make sure that each finger moves as a unit and stops the string in one movement. When working on a fluid 1st, 3rd or 4th finger action, model it on the 2nd finger, which invariably has a good action.
Make sure that the finger does not roll forward after landing on the string as this is unreliable for intonation and also pushes the finger too tightly into the string.
Practise repeated tapping of the finger from the air onto the string. Silent practice can also help concentrate the mind on the lift and tap down of the finger.
Left hand pizzicato with 4th finger helps develop the use of this finger as one unit, even though it uses a different finger action to the finger fall.
The thumb
The thumb supports the fingers, acting as a counter balance for their downward tapping action. Practise a passage with the thumb and then take it away to see how much the fluidity in the finger action depends on thumb support. This counterbalance does not need to be direct and the finger action functions best when the thumb supports the whole hand and is not unduly pushed back behind the 1st finger or under the neck. The thumb needs to rest against the neck without pushing against it so that it is available to move at any time. Shake out the hand and place the violin in between the thumb and the index finger without artificially moving your thumb to find a natural hand position. See Bring the Violin to You and Left-Thumb Placement
The thumb needs to support the whole hand frame including the 3rd and 4th fingers and not just the 1st and 2nd fingers. These exercises will help release tightness in the thumb and fingers:
Tap the thumb against the violin neck in practice breaks such as before or after a shift or after challenging passagework
Play with the thumb underneath the violin neck
Play with harmonic touch
See Release the Pressure
Placement of fingers
Finger placement depends on the size of hand and fingers, although in general the fingers contact the string a little to the left of the centre of the fingertip, seen from the players point of view.
In the early stages on learning we need to focus primarily on developing the hand frame as a whole. Later we need to pay more attention to the individual placement of the fingers, especially the 4th finger. Some 4th fingers bend outwards away from the 3rd finger at the last joint, which causes the 4th finger to strike the string very much on the outer (the bridge-side) edge of the fingertip. This is an issue for sound as well as reliability of finger fall. In this case it is important that the hand position is quite sloped so that the 4th finger lands at least towards the centre of the finger. See Galamian Principles of Violin Playing and Teaching, pp.17, 18,19.
Balance the hand
We vary our hand position depending on the context and the hand needs to be able to adjust to suit the demands of each task. Slow, lyrical passages need flatter fingers whereas fast passagework needs more curved fingers for clearer articulation. The hand also re-balances when playing a long low 1st finger trill (the 3rd and 4th fingers are away from the fingerboard as they are not immediately needed) and it is geared towards the best support for the trill. Similarly when playing a long, intense vibrato on a high 3rd finger we let the lower fingers release contact with the string since we want the maximum focus on the 3rd finger.
The hand frame also adjusts when playing double stops. When playing 3rds and 4ths the fingers are more rounded allowing the 4th finger to reach the lower string without it touching the higher string. When playing 6ths and octaves the fingers are flatter to allow greater stretch. When playing fingered octaves and 10ths we release double contact to allow more backwards stretch. Fingered octaves have a significantly sloped hand position while 10ths need the elbow to move substantially to the right in order to allow the 1st finger stretch a long way back.
Balance the fingers
For passagework we use all four fingers equally, and so the hand needs to be balanced so that it can support all fingers equally. As an exercise practise Scales in One Position (descending) and place all four fingers for the upcoming finger pattern at once. This helps teach the upcoming patterns to the fingers and also helps balance the weight throughout the hand. See Violin Left Hand, vol.3, Ch.11 Place Fingers Together for Speed
In slower, more lyrical passages there is more a feeling of exchange of weight from one finger to the next. Imagine walking the fingers to feel the exchange of weight and subsequent release in the hand.
When playing passagework at a moderate or fast tempo, the finger taps down onto the fingerboard and after articulating the note, bounces back slightly towards a harmonic touch to release any downward pressure. Practising with martelé bowing is helpful here. See Release the Pressure
Height of finger lift
Depending on speed and context, we lift the fingers high enough to allow them to tap back onto the fingerboard with the required amount of energy to stop the string clearly. The higher the lift and fall, the stronger the tap. Find the correct height of lift through listening for clarity of articulation, evenness and being able to repeat a passage reliably several times. If we lift the fingers too high then we may be late getting them back in time. If we lift the fingers too low the action may be spasmodic and jerky and the clarity of sound will suffer. Take care also that the finger action does not disturb the stability of the hand position.
The upswing is important. The quality of the upswing will lead to the quality of the finger tap back down. A tight lift will lead to a tight fall. Before we lift our fingers we need to know where they are going to land and in what pattern. Think of forming finger patterns in the air. Lifting the fingers in time with energy is especially important for playing passages of descending slurs with rhythmic clarity.
Trills
Although they are essentially ornaments, trills vary in musical purpose. Sometimes they represent virtuosic display; sometimes they intensify moments of great sadness in music. Consequently the colouring and speed of trill varies as well. To begin with, work on clear even trills at a moderate speed.
The lower finger needs to be securely in the string and the trilling finger needs to lift to the correct height. The clarity of trills often suffers when the finger lift is too low (causing the action to be irregular and unclear) or too high (causing the trill to be too slow).
Since the fingers naturally wander towards the indistinct middle, it is important to keep the half-step trill narrow enough and the whole-step trill wide enough.
Think about the bow, making sure that the point of contact and friction with the string is even. Adding a small bow accent can help articulation at the beginning of a trill. If you are changing the bow on a trill change it on the upper note of the trill so that the bow change is less noticeable.
At an advanced level and in some musical contexts we can add some vibrato action to a fast trill for added emphasis, however be careful not to do this until the fingerfall action is reliable and clear.
High positions
The angle of our fingers changes as we move into higher positions and the thumb stays at the throat of the violin as a pivot. As there is no double contact with the index finger, the palm of the hand against the side of the violin can give the feeling of a secondary support.
When playing very high we need to let the thumb leave the throat. Here we can let it follow the fingers and rest on the side of the fingerboard or come around and rest on the bouts of the violin. For both ways care needs to be taken to get the thumb back to the neck when shifting down again.
At times in higher positions, especially when playing 3rds with 2nd and 4th fingers, the nail joint of the finger can collapse to allow the finger to remain relatively upright and not pull the string significantly to the right. Take care with this however as vibrato is compromised and it is much harder to control the intonation with even a partially collapsed joint.
Horizontal finger action
When sliding the same finger from one note to the next, make sure that the touch is light and the movement fluid. Hold down the 1st and 3rd fingers on the string and practise sliding the 2nd finger back and forth between the outer fingers. Practice this also with other finger combinations as well as chromatic scales with the 1-1, 2-2 fingering.
Harmonics
Harmonics are used for special effect in all levels of repertoire and at times for technical purposes as a useful fingering. Natural harmonics tend to be played with flattish fingers, while artificial harmonics of the 4th use a more standard curve of 4th finger. When playing artificial harmonics practice the interval between the two fingers with stopped notes so that you can clearly hear the intonation
The harmonic requires the same point of contact with the bow as the stopped note of the same pitch. As this note is often high the point of contact will need to be close enough to the bridge. Make sure that the bowstroke is stable with even friction.
SEE
Bring the Violin to You
Left-Thumb Placement
Place Fingers Together for Speed
Release the Pressure
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