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You need to build up the muscles you need to push down the strings. Keep a clothes-peg in your pocket, and in idle moments do this exercise. Do everything as slowly as you can manage to educate brain and muscles. If it hurts, stop and try again the next day.
Step 1First finger
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Take the open ends of the clothes-peg between the TIPS of left hand finger and thumb. Without any help from the other fingers, slowly close the clothes-peg together. Now allow it to open again - as slowly as you can. Repeat 5-10 times.
Also, I assume that these exorcises would benefit any string player? I myself play the cello, not the violin.
Yes - it should help for cello (or any other sting instrument) as well.
NB: These exercises are things you can do when you're not at the instrument. Obviously, they are not a substitute for playing!