The original post was asking about guidelines when you have a lot of new people. I think it can be really tricky for a lot of reasons

1- Beginners often want to play and don't know any session etiquette at all. They may be inhibited about joining in and feel left out or unwanted. Conversely, they might be much too brash and not realize they are stepping on toes. So beginner bodhran players sometimes pound on away loudly on every set or guitarists apply the same set of chords before learning the melody, or try to accompany a song that is meant to be sung unaccompanied. Or they bring out song or tune books in a session that expects the tunes and songs to be learned at home.

2. Different genres have have different unwritten rules- for example the blues session Steve described and the bluegrass sessions described by Barbara. Old-time and Irish sessions are inclusive- all the instruments play together (no breaks), but have their own little internal rules and dynamices.

So musicians crossing the line to a new genre may have expectations that don't mesh with the session- for example, playing bluegrass chords on a mandolin in an Irish session.

3. Even within a genre, different sessions have different personalities- how tunes are started, how much the "alpha musicians" control the flow etc.

I am an "anchor" musician in two sessions- one strictly Irish and one that is much more ecletic. We try to be welcoming to all newcomers, but sometimes have had to redirect people. It's not easy- how do you tell someone that their choices are inappropriate for the particular session without hurting their feelings?

I had to do this recently and it wasn't easy. I was very direct in saying things like "This is the Irish session, and usually in Irish sessions people__________________________. But at the other session we hold, we play all kinds of music, so let's play that one there".
I think I might have been too blunt for a couple of people. One felt like we were just too fast for her, even though we encouraged her to return. One person disappeared, and another person seems to have taken some of the suggestions to heart.

Here are a few things I think can be done:
I think it's possible to have conversation during the session and talk about it without singling someone out- like "One thing I've always enjoyed about this session is the way we ________________"
Another idea is to take a person aside and say some encouraging things and suggestions about fitting in better at the same time, like "I'm so glad you've come back to play here. Have you ever tried watching the _________ accompanies the song?".

Of course some people don't get subtle hints, and if it's important, it needs to brought up directly or be willing to tolerate it. If that dobro shows up at the Irish session again I'm planning to be very direct!

Hope this is helpful and to the point....

Sharon G