I'll add when you are playing, don't keep going if your writsts start to ache. Fiddle playing is very physical, and you can strain things. If you start getting aches, tension or sluggishness in either hand, put the fiddle down and shake wrists, hands, arms about a bit to loosen up. Play for shorter periods - don't spend long hours at the violin in one session, you may be overdoing it! I started out classically trained (ish) and started folking a few years back (I'm no professional, but I play a lot)thre are proper 'classical' ways of holding a bow, which many self taught peeps don't know about/bother with. There are better ways of holding a bow, but I don't beleive in the 'one true way' theory. The important thing to do is make sure that the way in which you hold your bow is relaxed and balanced. Pay special attention to what you are doing with yourlittle finger - if you hold the bow of its centre of balance, you can put a lot of strain on that finger as it applies pressure to keep the thing in balance, and that impacts on the rest of the hand, and the wrist.

I would suggest though, treat fiddle playing like you might any athletic sport - warm up, take time for breaks, don't overdo it and be very wary of any injuries and treat any occuring with a lot of respect.