Some very good advice contained in the above answers.
I tried in college, and was a total wash-out: really awful.
One practice technique that might help to improve your sound more quickly, because I think proper "bowing" is probably the key to producing a good sound:
1) start with the c-major scale, and then proceed on thru them, each successive one with more accidentals than the preceding.
2) take each note separately. And just bow(only, repeat, repeat, repeat) - very slowly at first - and close your eyes; and listen, and pay attention to to how your holding the instrument, the pressure applied by the fingers of your left hand, and take particular note of the areas of your body, which are tensed.
3) always practice with as much relaxed a manner as you're capable: tension of any kind, is what usually defeats any instrumentalist(or vocalist for that matter), in mastering their performance technique.
Good luck,
Alberich