"Practise slowly and listen for resonance. Play in rhythm but at half tempo. Finally play in tempo."
Practise intonation in different tempos:
First play slowly without worrying about rhythm, taking as many bows as you need to listen for the maximum ring of each note. You can also watch for the sympathetic resonance on open strings, you'll see the string vibrate in increasingly wider vibrations. The wider the vibration of the string the greater the resonance and the more in tune the note is.
Then add rhythm, usually at quarter or half tempo. Repeat as many times as needed listening for intonation and thinking how to improve it.
When you finally play in tempo take a short listening break after each playthrough to check if any notes need improving.
- for The Art of Practising the Violin by Gerle