I’m a “classically trained” violinist, and I’ve been going to fiddle jams for a while, now. Nowhere near good enough for anything, in part because I have a hard time playing by ear (I call it “tune” deaf), and my memory for tunes isn’t good enough, yet.
That said, the fiddle sound is characterized by playing legato and detache, with accents and note ties determined by the beat of the tune – most are dance tunes or based on dance tunes, so your accents should be something to dance to. 🙂 Other characteristics of fiddle play – swinging the eights, droning on neighboring strings and double stops, sliding up or down into the note, various kinds of grace notes, depend on the style of the tune you’re playing. There are many fiddle traditions, and each has their own style. I think it’s best to start with one and get familiar with it before going to the next, rather than trying to learn them all at once, if for no other reason that there are just too many of them.
Do not mess with cheap strings or other gimmicks. 🙂