Practise these exercises without the bow:

• Drop and lift your 3rd finger on and off the A string. The movement should come from the base joint of the finger.
• Alternate between your 2nd and 3rd fingers, then between your 1st and 3rd, only putting one finger down on the string at a time. Imagine that your fingers are marching up and down on the spot.
• Lift and drop your 3rd finger while your 1st finger remains down on the string, then while your 2nd finger remains down.
• Repeat these exercises on the other strings remembering to move your elbow under the violin as you change string so that your hand, wrist and forearm stay in line.