As you start to play, aim for solidity in left and right hand.
Your left hand should feel full, fat contact with the string; the hairs of the bow should sit thickly and exactly on the string..
Compare the solidity of contact in your hands with the solidity of your feet on the ground.
Try it with double stops as well.
Practising with a mirror is extremely useful – for both hands.
However, one must not become too self-obsessed.
When practising with a mirror, try to position yourself so you do not see your own face.
You will gain much in the way of objectivity
As you play, your left and right hand are brought together not only by the bow and the string.
Your arms, the bow, and the string make a complete circuit with a Pac-Man shape.
Energy can flow freely in this circuit.
Play a slow scale, watching the small part of the string between the bridge and the bow hair.
Each time you draw the bow, you will see the string push to the left (for up bow) or the right (for down bow).
Do your best to maintain this angle in the string as you play, like an archer in perpetual preparation to shoot an arrow. The string will take care of the rest.
The string is the bow; the sound is the arrow.
The energy of the string has an outlet at the bridge.
Watch the bridge drink the string motion (audio in). Feel the instrument’s resonance as you play (audio out).
The invisible motion of the bridge becomes the sound of the instrument.