You’ve been given good advice so far; bring a book or two, dress comfortably (although I’d recommend more than jeans, less than a suit – something that you feel comfortable in that demonstrates a respect for the judicial system).
In case it matters to you and you make it as far as voir dire, there are a couple of different ways that a jury can be seated. Generally, a juror can be struck “for cause” or a party can use a “peremptory” challenge to strike a juror. Being struck for cause means that the party striking you as a juror has a legally valid reason – you are related to one of the parties, for example, or you’ve answered a question in a particular way (i.e., it’s a car accident case and you were in a car accident last week). A peremptory challenge can be used to strike a juror without cause – essentially, the lawyer for one side or the other doesn’t like the cut of your coat. Of course, a peremptory challenge cannot be used to strike you for an illegal reason – race or gender are primary examples (a so-called Batson violation).
So those are the two bases for striking a juror. Each side gets an unlimited number of strikes for cause (which makes sense; the judge rules whether the “cause” alleged is sufficient to justify striking the juror, so the system doesn’t get abused), but each side usually is limited in the number of peremptory challenges it can use. If the number the judge permits is three peremptory challenges (which isn’t atypical), you have to use them wisely.
Many courts use what is called the “Arizona method” of selecting a jury. If the jury size for trial should be 12 jurors with 2 alternates, and each side has 3 peremptories, the judge will seat 20 people in the jury box for voir dire (12+2+3+3). The judge will then ask questions of the jury. At the end, each side will approach the judge with their list of jurors they want excused for cause, and those they want to challenge peremptorily.
What some judges will do is permit each side to go one by one, announcing which jurors they want to strike. You can see how this would prolong jury selection: if the plaintiff strikes juror 3, and the defense also planned to strike juror 3, once the plaintiff announces he wants juror 3 striken, the defense will go to its second choice. You could conceivably exercise all 6 peremptory challenges. Since there may also be challenges for cause in the group, additional jurors may need to be seated and voir dired.
What most judges I have seen will do, then, is to essentially require a secret ballot: each side writes down their peremptory challenges, and never knows who the other side wrote down. The judge simply reviews the lists and announces which jurors are striken. As lawyers, of course, we dislike this method because it means that we have had to “waste” a peremptory on someone the other side wants to strike.
Anyway, the “science” of jury selection is fascinating to me. I’m sorry to say that I’ve never been called for jury duty. Odds are good, of course, that I’d never get on a jury, but just being able to see it from the other side of the bar would be interesting.