Darol Anger's 8 Paths of Improvisation: on the violin
Darol Anger has developed a few interesting techniques for fiddle improvising and he teaches online and there are loads of videos of his lessons on youtube. he's one of the people who developed the 'chop bowing' technique, which is kind of a percussive rhythm improvisation that goes way beyond the usual bluegrass 'chop' or 'chuck'. I'll be posting a bunch of videos on that topic. Casey Driessen is another fiddler who extended that technique and i have a video of him already here. Here's a cool series of ways to think about improvising: