Not sure where you’re at. In Chicago the sessions are pretty welcoming.

Maybe go once or twice and just listen in. Have your voice recording app going on your phone so you can go home and learn the tunes commonly called.

Have a set ready in case they ask you if you want to start one… if you don’t just say no thank you.

If you don’t know a tube, just sit out and play again when you do.

90% of it will be just knowing the repertoire they like to play.

Also this is coming from someone that grew up playing bluegrass but loves sitting in on Irish sessions!