The left hand frame needs to be set up for long-term and varied demands. At all stages of learning we need to be developing hand positions that eventually will be able to execute complex patterns at speed with high levels of accuracy. We may spend many years of study working on issues such as developing the backward stretch of the 1st finger, developing a reliable 4th finger action without locking any joints in the finger and not rolling the hand from the wrist while playing basic finger patterns. See Introduction to Finger Action
Having the violin cradled between the thumb and the index finger in the lower positions helps stability in fingerfall and shifting. There are times where we release this double contact: while vibrating, when preparing to shift up on the E-string into 5th position or higher and for extended hand positions for challenging chords, but it is important to return to this double contact after the need to release it has passed. Sometimes double contact is not so useful for players with small hands, since swinging the elbow to the right bringing the index finger away from the violin neck can give greater stretch. However having the violin sit low in the left-hand cradle so that the fingers are relatively high above the fingerboard can also give greater stretch while maintaining double contact.
The left arm swings under the instrument while crossing from the G-string to the E-string and back. This allows the hand frame and fingerfall to remain approximately the same on all strings. The arm also swings to the right while shifting up to 5th position and higher, and back to the left when shifting down to 3rd position and below. The swing of the arm to the left helps unlock tightness in the whole arm and can be a useful preparatory movement for shifting up.
Finger before bow
This is worthy of systematic practice as many coordination issues come from late left fingers. Use pizzicato and martelé to practice tapping the finger down well ahead of the bow. Try having one player controlling the bow while another places the left-hand fingers. Make sure the left finger is calmly in place before beginning the bowstroke. See Finger Before Bow Schradieck
Be aware of your hand size. Players with smaller hands may need to avoid extensions and shift more often while players with large hands, especially large, thick fingers, may need to be careful with contraction fingerings and also need to find alternate fingerings to avoid playing sharp in very high positions.
Thinking in patterns
Fast passagework, such as in Paganinis "Moto Perpetuo", consists largely of the four basic finger patterns in various combinations. Practising these patterns from the beginning will help our facility. Regular practice of scales and other exercises can help develop reliable knowledge of these patterns. See Finger Patterns Demonstration and Finger Patterns and refer to Robert Gerle, The Art of Practising the Violin.
Technical timing is the making of preparatory movements at the right time and speed for any technical task. These preparatory movements need to be appropriate to the speed, rhythm and above all the musical character of the work. For instance, while jerky shifts are technically unreliable, they also disturb the musical line that we want to project. See Wronskis edition of Kreutzers 42 Studies for discussion of this issue, also Galamian Principles of Violin Playing & Teaching, p.23 and Gerle The Art of Practising the Violin.
We need to hear what we play
There needs to be a basic level of resonance and clarity in the sound when we practise if we are to work effectively on intonation and articulation. Often focussing on a consistent, resonant sound can considerably help our work on intonation and coordination.
Finger Before Bow Schradieck
Finger Patterns Demonstration
Finger Action - Introduction
Facility - Finger Patterns
Resources - Bibliography