QUOTE(Ellie Rose @ Feb 26 2009, 07:07 PM)

I play violin, and I get muscle pains in my left forearm if I play for longer than usual, and sometimes just after normal practice. Is this normal? Can I do anything to help prevent/ease it?
Probably caused by unnecessary tension in your wrist or elbow (or both). You should focus on allowing your arm weight to drop through your elbow to the floor, ensuring your forearm is perpendicular to the ground or slightly to the left, but never to the right (except in 6th pos+, depending partly on hand size and joint flexibility). Also try to take "posture checks" every 10 mins of playing or so, just put your violin and bow down and completely relax your upper body, a la Alexander Technique. Really, you need to look at your basic technique though, to solve this long term. If by "longer than usual" you're talking in the range of 4h+ in a day, or have recently increased your practice very dramatically, then perhaps it is to be expected occasionally, but otherwise you should be able to rid yourself of this pain with the help of a good teacher and maybe some AT lessons.
QUOTE
Also, has anyone got any tips for speeding up calluses? I've started teaching myself acoustic guitar, so my fingertips are sore which affects my violin playing too.
Left hand pizzicato and glissando scales. Have fun with those

See Ricci's book "LH Technique" for superlative exercises in both areas.