Listen, listen,listen. Don't play loudly, especially if you don't know the tune. Ask the pub owner ahead of time if it is open to all and then ask the players. I found only one session in Adare that was suppose to start before 10. Remember sessions are times to chat about music as much as to play, so you may not be about to follow the conversation at times. Often sessions are times for people to catch up on music or personal news since last week. If you feel tension as you enter the group or they tell you they play in some strange tuning or it seem to be waiting for a friend before really getting down to music or ignore you between tunes, you may be in a close group.