A folk session in a pub will normally comprise at least three musicians or singers, rising to a couple of dozen players or even more. A certain degree of etiquette is always appreciated and this becomes more important as the number of players rises or as new and perhaps inexperienced players join in.

The following guidelines are not comprehensive but cover some of the most commonly followed courtesies:

1. On arriving at a session venue you will almost always find that seats have been reserved from a certain time. If you arrive early, it may be unwise to simply choose the best seat since a session will sometimes have regular players who always sit in the same places. I believe this is more common in Ireland than in the UK but if you are a newcomer you may like to think twice about sitting in the centre seat, anyway. You are likely to end up surrounded by the best players in the house and chances are that you won't feel too comfortable. See also note 14, below.
2. 
   There will normally be one or possibly two lead or key members of the session, frequently the oldest and/or most experienced. The key player will normally begin by choosing the combination of tunes in a set and setting the pace, and it is considered bad form to join in and then speed up or otherwise vary the rhythm or pace of a set.
3. Commonly the key player and others who regularly play in the same session will begin by playing well-known sets of tunes which others can join in with. Once a session is under way, the key player will normally invite each other player to contribute a solo set of tunes or a song. If uncertain whether to join in or not, newcomers should be guided by the regulars - sometimes sessions encourage all to join in on more or less everything, other sessions are more formal. The golden rule is, if you are unsure whether to offer an accompaniment or not, don't.
4. A newcomer should be aware of the arrangements for playing or singing and it is generally considered impolite to jump in and sing a song or play a tune without being asked, or to break an obvious sequence (eg "clockwise around the room").
5. The normal arrangement for solo performances is ONE song or tune or set of tunes in your "turn". You are unlikely to be popular if you hog the limelight by playing another set or singing a second song when everyone else is only singing or playing one, unless you are invited to do so.
6. If you are going to play or sing mainly - or only - material which you know, and which others are unlikely to know, be prepared to pass on the names of tunes and songs and possibly teach others how to play the tunes as well. It is often considered bad form to perform only obscure material which no-one else can join in with, and then decline to offer it to others.
7. If you play in a band and all the members of that band go to a session, remember that this is not a gig for your benefit, and experienced players will not be impressed by you showing off your clever arrangements, because others will not be able to contribute. A set piece now and again is fine but remember that a session is a community thing, and not everyone may enjoy your band as much as you do.
8. In an Irish session, bodhran players should use some commonsense and be aware that not every song and tune requires accompaniment. Not all players welcome percussion, and the principal complaint in Irish music sessions tends to be that there are too many bodhran players, they are too noisy, and cannot be made to put their drums down for a while. If you are one of several bodhran players at a session, be prepared to defer to the most experienced player and do not assume that every performance requires your accompaniment. Most sessions prefer one or perhaps two bodhran players at most, of which only one playing at any time, and are appreciative if the bodhran player keeps the volume of their instrument in balance with the rest of the instruments. The bodhran is an accompanying instrument by and large and discretion in volume is much appreciated.
9. If you have a very loud instrument, eg a banjo or piano accordion, it is courteous to avoid sitting next to a player whose instrument is quiet. They will have difficulty hearing themselves. This is especially important if you have a "sided" instrument such as the accordion, since the person on your left side will hear your bass playing very loudly.
10. Depending on the nature of the instruments present, try to find at least some tunes in a key in which others can play. Some instruments, eg whistles, concertinas and melodeons, can be limited in range and if you are, for example, a competent fiddle player you might like to consider the keys of D and G now and again and not choose A all the time or opt for even less common keys. The most common keys for playing Irish and English folk music are G, D, A, C and the relative minors, Em, Bm, Am and very occasionally F#m.
11. NEVER record a session without permission. Many players also do not wish to be filmed or photographed. If you want to record the event in any way, you must ask the key player first.
12. Do not expect to be paid or to receive a free drink as a matter of right. Arrangements between the session musicians and the pub landlords vary widely. There is generally no harm in enquiring if a drink is likely to be on offer, but never expect any kind of gratuity simply because you are there.
13. Do not attempt to learn a tune whilst it is being played by others. There is nothing more irritating than someone who can be heard groping for notes, phrases, and occasionally even keys whilst others are playing. This especially applies to guitarists "hunting" for chords. The time to learn a tune is in a break when no-one is playing, and in a good session there should be at least one such time. In Irish sessions I understand that time is reserved between tunes for this purpose, traditionally.
14. Lastly, there are a few places where you may still find a session run by the local musician or singer in a village, who may have held that position for many years. In some cases it is considered discourteous to sing the songs or play the tunes associated with the local singer or musician, and sometimes even to accidentally sit in seats which have been sat in by the same "regulars" for many years. In these types of get-together you will often see that the musicians leave their instruments outside, or in the cases, until they have had a drink or two and/or until the most experienced players have begun to play. The best thing if you suspect that you are in this kind of situation is probably to buy the key player a drink or two, and discreetly ask around to find out what the rules are.

Sessions should be welcoming and relaxed and FRIENDLY. This is often, but not always the case, and you must use your own judgment in deciding whether you like a particular session, the venue, and/or the other players. It is probably wise for a newcomer to visit a session perhaps three or four times to see how it changes over time, before making any decision to go elsewhere. If you are an inexperienced player, a good session will give you space to show what you can do and will make you feel welcome regardless of your level of skill, as long as you excercise some discretion when you join in with others. If you are an advanced player, it is polite when accompanying others to show a little restraint - even if you can play faster and with more variations than others, remember that unless it is your solo spot you are an accompanist for other players. Don't outplay someone on their own performance, this is very bad form.

Above all, have fun, meet new people, learn new material and keep folk music alive!!