I recently attended my first jam, fortunately there were multiple people there, so any mistakes I made were well covered up. 🙂 I think having a basic knowledge of what tunes will be played helps a lot. I’m just barely at the level where I can figure out what key the song is in and can follow along sight reading if they play slow enough or have enough repeats.
Of course with fiddle tunes there’s a million and one variations of every tune. Just remember, fiddle jams are supposed to be fun, no one’s gonna hate you if you miss a note or two or even sit out a song.