That's a tough one, not having heard the group, or you play. Maybe I'll have to shoot by one of these jams. I live in Pdx, too. I guess I'd say only play on the tunes that you feel that you know, unless it's a simple blues or something. Observe the rules of etiquette for jam sessions, which have been written about here, I think. The free association thing can work, too...I mean everybody uses quotes sometimes in their improv. Yeah, it's too tough to make any meaningful suggestions w/ the limited info. I'll try to come by. Oh, yes... Practice!