If you've never attended a filksing before, you're twice welcome. Don't think that you have to pretend to be a bump on a log just because you don't know the titles of any filksongs. When your turn comes round, feel free to ask for a song about your favorite SF book or TV show or movie. Or to ask for a song about spaceflight or fantasy or computers or fantasy gaming or fan history.
If you don't understand a reference in a filksong, ask politely once it's over and someone will be glad to explain it to you. Or if you'd like to sing a favorite song that seems to you likely to interest other SF fans, then go ahead and do that. Or if you've written a song that goes to a well-known tune and you don't trust your own singing voice, you can probably find someone willing to sing your lyrics for you.
POKER CHIP BARDIC
If you've never attended a Poker Chip Bardic before (and that's likely), here's how it works.
When you come in, you'll be handed three poker chips: Red, White & Blue. We'll sing a Red round, then a White round, and then a Blue round.
As usual for a Bardic, you get to Perform or to Pick a song or singer once in each round. Unlike the usual Bardic, the turn doesn't pass clockwise or anti-clockwise around the circle. Instead, when a song is over, anyone who still has a chip the right color for that round can toss it in. That person can then perform a song or ask a certain person to perform a song or ask if anyone present is willing to perform a song (specifying the song somehow -- or asking for any song that applies to a general subject). This lets a song flow naturally from the previous song, letting a set of songs develop in the Bardic Circle just as it can in a Chaos Circle, while still preserving the basic egalitarianism of the Bardic.
If you have a follower song you'd like to sing but you don't have a chip left, announce that you've got a follower -- and see if anyone tosses in a chip to hear it. If not, then abide by the group consensus.
FORTUNE COOKIE BARDIC CIRCLE
In this variant, each performer chooses a slip of paper which bears the name of a subject on which a number of filksongs have been written (e.g. Vampires). We'll then go once around the Bardic Circle with each performer singing a favorite song that has some relationship to the subject he has drawn. (Yes, it's OK to trade subjects with someone else.)
In a Chaos Circle, there's no set order of who's going to sing next or any attempt to make sure that each filker sings the same number of times. Non-singers might suggest a song or topic, but the Chaos Circle is really for singers and those who want to listen to them.
That doesn't mean that all songs have to be filksongs. Folksongs are welcome. So are all other songs that seem to fit in. If you're not sure that a particular sort of song will be welcome, feel free to ask.
If you've never sung in a Chaos Circle before, sit quietly for a few songs and see how it works. You'll notice that once a singer is finished, there'll be a few moments of silence. Then one of the other singers will strum a guitar or say, "I've got a follower for that" or do something else to indicate a readiness to sing. If more than one singer is interested, then the next singer may be the one with the fastest reflexes -- OR the matter may be decided by whoever's in charge of the Circle.
All the people in the Chaos Circle room may seem to be old friends. That doesn't mean they won't be interested in hearing you sing. Wait till someone does a song that seems like a good lead-in to one of your best songs, and then go for it. By the end of the convention, you may find you've got a whole lot of new friends. If you don't feel self-confident enough for the Chaos Circle, you should check out the Bardic Circle. And then think about coming back to the Chaos Circle after 2 AM when there are fewer people in the room and when a new face (and voice) will stand out more.
DOMINO CHAOS CIRCLE
In this Circle, each song must somehow relate to the one it follows just as a domino tile must match the tile it touches.
The song may have the same subject as the previous song, or the song may have the same melody as the previous song, or the song may have the same author as the previous song, or the song may be a rebuttal to the previous song.
No singer may perform two songs in a row any more than one player could take two turns in a row when playing dominos.