Being a moderator is not unlike being an ideal host, graciously guiding a conversation while always keeping in mind that you, as moderator, are there to make everyone else on the panel look good, and to make sure that everyone in the audience has a good time. This is usually easy to do, as most panelists are intelligent and well-informed and often witty, and the Readercon audience is friendly and often as knowledgeable as the panelists (sometimes more so).
Prepare yourself ahead of time. Email the panelists in advance to get everyone's take on the topic. Have questions and notes, and have paper and pen or tablet handy to jot down new questions that come to you as the panel progresses. Bring an unobtrusive timepiece.
When you get to the panel room, introduce yourself, make sure everyone on the panel has a glass of water, and introduce them to one another (if they haven't done so already).
Start on time, even if a panelist is late. Ask everyone, including panelists, to turn off mobile phones and other noise-making devices for the duration of the panel.
If you introduce the panelists to the audience, make it interesting—don't just read what's in the program book—and brief. You can also let them introduce themselves and give them a chance to flog product. Some will seize the opportunity; others will shrug it off. But exposure for one's brand and projects is one of the reasons why panelists show up at cons. At the very least, this may help prevent an aggressive self-promoter from hijacking the panel into an infomercial about their work later on.
After the intros, ask a question that interests you and give every panelist a shot at addressing it. If you have chosen well, other questions or issue will arise out of the initial question. But it is important that everybody gets to stake out their territory at the start. Rather than waiting for the panelists to respond at random, point to an individual and ask them what they think. This is less awkward than having everyone answer at once (or having no one answer).
Move on from turn-based responses as soon as possible. If each question/issue has to march down the line in the same order, the audience and panelists can zone out. You can ask follow-up questions to someone who says something brilliant, outrageous, or wrong. Keep everyone guessing who will speak next.
Make sure everyone on the panel gets airtime. Make sure everyone is polite, to one another and to the audience. Don't hesitate to shut down someone who's being rude. (See "troubleshooting" below.)
Above all, promote conversations. On every panel there are loud voices (brash) and soft voices (shy). Try to average the overall volume out. That means creating openings for the shy and reining in the brash. The brash are not always the most interesting, but the shy will quickly give up trying to speak, in which case the conversation you are looking for might devolve into dueling monologues. As a moderator, whenever you get the chance to pose a question to the panel, consider tossing it to the shy panelists. The brash will always find a way to speak.
It's often more interesting when writers talk about their influences or their research than when they discuss the nuts and bolts (plot, characters, etc.) of their own novels. It keeps the ball rolling, and gives the panelists the chance to find common ground, or share different approaches to the same topics.
Have enough questions prepared to get through the first two-thirds of your allotted time. That usually means about five or six, including one that is designed to spark controversy. Save that one for the half-hour mark, at least.
Leave some breathing room for new ideas to emerge. If a panelist brings up some intriguing aspect you hadn't thought of, be prepared to run with it—that's often when the most interesting discussions arise. But if things go completely walkabout, bring it back to the panel topic by interjecting one of your prepared questions.
A good moderator keeps things moving but mostly stays in the background. Your job is to make the panelists look smart. That doesn't mean you shouldn't be informed and amusing, but don't grandstand—you can do that when you're a panelist, thus providing another moderator the opportunity to do their job. If you're leading the discussion (moderation + participation), make sure not to take more than your share of speaking time.
Above all, have fun. Smile and make jokes as appropriate. When someone says something really smart or insightful, underline it for those who might have missed the point. Make friends on the spot with any interesting panelists you've never met before.
Have a few unusual questions or fun facts to trot out in case of moments of silence or awkwardness, or in case things totally go off-topic.
If a panelist can't get a word in edgewise or strongly disagrees with where the discussion is going, gently steer the conversation toward them.
Sometimes you have to shut down a panelist or an audience member. It is okay to interrupt when needed, and as moderator you have to right to declare it is time to move on.
If someone just won't shut up (it happens), wait for them to take a breath, then jump in. If someone really, REALLY won't shut up, cut in and say, "Let's give someone else a turn—Baal, what are your thoughts on human sacrifice?"
The ability to be disarming can be very useful if things get heated. So is the ability to take charge if someone speaks too long, is rude or inappropriate, or just boring. If you're in doubt (Is it only me, or has Lucifer been talking nonstop for the last seven minutes?), you can usually take the measure of this by glancing at the panelists and also the audience (to confirm that you're not the only one who's bored/appalled/restless). Then turn to someone else on the panel and say, "Raphael, what do YOU think about the problem of Evil?"
You can also pose a completely different question so that the conversation goes off on a new track. You don't want to belabor one topic for an entire 55 minutes. Declare that whatever snag you are trying to get around is "an excellent topic for another panel," and move on.
If at all possible, do not take questions from audience until you're about 40 to 45 minutes in. The Readercon staff have chosen your panelists with care; the audience is self-selected. Some don't have a clue; some will be argumentative. An overly vocal audience often leads to topic drift.
That said, if things are going slowly, or you've run out of ideas, or the audience is leaving in droves, go ahead and open it up for questions earlier.
The Q&A time is often when someone will ask an individual panelist about their work ("Lilith, how much of an autobiographical element is there in Genesis?"), which is another reason to keep the prior discussion open and less specifically slanted to an individual panelist's work.
You as the moderator choose which audience members speak, and when. Ask them to stand if they're able; in a larger room, there may be a staffer who can give them a microphone. After they speak, you should repeat the question (to make sure you heard it correctly, to make sure it's audible on the panel recording, and so everyone else can hear it), then turn it over to the panel. Here too it's important to be equitable: recognize people from both sides of the room; from the front and back of the room; of different ages and genders and ethnic backgrounds and abilities. Identify questioners by visual elements ("Yes, third row, in the blue shirt") rather than guessing genders.
This is when the discussion can get really interesting and go off in unusual directions. Take notes for future panels!
A Readercon staff person will hold up a sign warning you when you have five minutes left. That's your signal to call for one last question, ask the panelists for closing remarks, or otherwise bring things full circle so that everyone goes home happy. This is also a good way to extricate yourself from sticky audience interactions. This can be the time to go back to turn-based response.
Thank the panelists, thank the audience, and leave the stage promptly so that it can be set up for the next panel.