It's not real complicated, mostly it is about having fun!! Common sense and common good manners are the important thing to remember.
Irish music is very melody oriented and the melody should always take precedent. So, if a number of bodrans or guitars show up, by all means play!! But keep in mind that you don't want to drown out the melody. Sometimes it is necessary to take turns.
Also this is an Irish music seisíun, occasional other kinds of tunes are just fine and often fun, but the focus should remain with Irish music. Hammered Dulcimers are often (sadly) banned at Irish seisíuns, but hey, I play one so all are welcome.
There are three main kinds of seisíuns, Open, Closed or Slow.
Open Seisíuns, means just that - anyone can join in, though you need to have basic skills and know a bunch of the tunes. Sometimes there is a seisíun leader who helps keep the flow going. The seisíun leader is often the organizer of the seisíun or maybe an outside-the-area well known musician who is invited to lead the seisíun and help attract other musicians, or maybe just the eldest and well respected player there! Our seisíuns are Open Seisíuns!
Closed Seisíuns are by invitation only, sometimes by paid musicians and it is often really a performance but less formal than a true concert or stage performance. These are very common in Ireland and in some of the big cities in the US. Sometimes it is hard to tell if it is a closed seisíun - hidden microphones are a clear giveaway! There is a bar in Boston where the musicians sit around a table and the light right over it has microphones, they also play in Fb diminished minor, so it's hard to join in with standard pitched instruments anyway. When I asked, I was told that it was not really a seisíun. Usually the musicians at these kinds of seisíuns are really good so they are worth listening to.
Slow Seisíuns are mainly for beginners and easier tunes at a slower pace are played to accommodate people just learning the music.
Here are some Do's
--Tune your instrument! Many musicians use electronic tuners and use A440 and even temperment as the tuning standards. Uilleann Pipes use just intonation so a couple of their notes are a little different, just part of their charm. Some pipers like to play their drones in dissonant keys. I like drones.
--Try to bring an instrument that is in the same volume range as the others or is able to be muted. Hey, I have heard traditional Irish music played on saxophone! Amplification is not usually used, the one exception is an electronic piano/keyboard. Keep in mind that it is easy to turn the volume up to loud. Controlling the dynamics of your instrument is one of the hallmarks of a developing musician and takes some practice and skill. Unfortunately, beginners, who should have the quietest instrument so they can hear better, also need to hear themselves more. One of the ironies of music.
--Try to have a tune or two that you are comfortable starting. Try to think up two or three tunes that sound good together. They are called "a medley" and musicians (and others) like to hear interesting changes. It's fun to get to start a tune. If no one joins in, play it a couple of times through and move to another tune. Seisíuns are not just about playing tunes you know, but also sharing really cool tunes that you might have found.
Be friendly and make friends. If there is someone you don't know introduce yourself. If you are new try to introduce yourself. Some a little early and socialize. Usually musicians will drift in and out of the music playing to talk.
--Take turns. This should be informal and not school-like. Going around in a circle is NOT usually done. Remember this is primarily a social occasion. If there is a seisíun leader, they will guide this, when needed. But you can help, too. If you notice someone hasn't been playing, try starting one of the more common seisíun tunes.
--This is a social occasion, talking is OK! Just don't disturb the seisíun. If a tune is going on, keep it low. Tunes don't usually rattle off like a machine gun. Remember this is a social occasion. If someone is singing, however it is usually considered impolite to talk and if you don't notice at first someone will tap your shoulder.
--If you sing, let it be known. Since this is not primarily a singing seisíun, let people know that you sing. At some points in the seisíun a song will be called for. Go for it.
--Where to sit. There is usually a core group of players who play in the inner circle. If you are a beginner or new, it is customary to sit toward the edges of the group. Bodhran players should normally sit toward an edge. If you bring someone who does not play, they should not sit with the musicians!
--Do have fun. Remember it's not just about the music it's about enjoying yourself with friends.
--Do play your bodhran gently, you want to make sure that the musicians next to you can hear the melody. Playing a bodhran is no excuse for not knowing the tunes. While it is a good way to have minimal musical and still join in, practice at home, learn your instrument and play WITH the tunes. Learn the different kinds of jigs.
--Do listen A LOT if you are a beginner. Going to seisíuns is a good way to learn the music. Take advantage of the expertise of the other musicians. Some of the musicians who regularly come to our seisíuns are well known professional musicians. We have one musician who is a Comhaltas Hall of Famer. Most musicians are more than willing to share their knowledge.
--Don't play out of tune. Bring or borrow a tuner, if you need to. Some of the instruments are fixed pitches (concertina and accordion for example), but are usually pretty close. Flute players remember your instruments go sharp as you play them. Do the best you can, but this is not a concert hall so don't obsess.
--Watch your tempos. Don't speed up and when you come in come in at the same tempo. Let whoever started the tune pick the tempo.
--Don't keep starting esoteric tunes that no one knows. This is not a recital. But do share a tune or two. Eventually someone else will learn it. Spreading and sharing tunes is an important part of a good seisíun!
--This is not your living room, so practice at home and not at the seisíun. If you start a tune and can't quite remember it, making a couple of attempts is OK, but after that give it up and practice it at home for the next seisíun. But, also, it is OK to make a mistake.
--The house will often buy a couple of pints for the musicians to show their appreciation to the musicians. But don't get drunk. It makes most peoples' playing sloppy which is less fun for the people around you. I was recently told about a seisíun somewhere in downstate NY, where one of the musicians made a derogatory comment about the generosity of the pub owner, they now have no seisíun and the local musicians are trying to find a new venue. Traditional music is usually not a big moneymaker. Be appreciative of your host and especially any servers or bartenders who have helped you.
--Unless you are the seisíun leader, give other people a chance to start a tune. If someone else starts a tune it is customary to let them put it together with another tune to form a medley. If you have a great idea for a medley, just say, "I usually put that with ______" afterwards.
--Don't get upset if someone breaks the "rules." They are guidelines for having fun. People have different social skill levels and we all get cranky now and then, so relax and enjoy yourself! We are all friends here having fun together!
--Keep your "diddling" down. If you don't know the tune and have a loud instrument it can be very distracting for those who know the tune. Some people are better at this than others. If you want to try out someone's instrument or are trying to remember a tune take it away from the main music area.