1. Never spend more than 10 minutes on a deck check. You should actually try and finish a deck check in 5 minutes or less. A good rule to follow (and the rule we follow at Pro Tours) is once 5 minutes has elapsed for a deck check, immediately return the deck to the player, regardless of whether or not the deck check is completed. Even if you are only halfway done the deck check, it is important to delay the tournament as little as possible - unless of course you believe there may cheating or deck manipulation involved. Since you should always give a time extension to players who get their decks checked, you should do everything possible to keep the checks as quick as possible. Use appropriate strategies to reduce this time and train judging staff as much as possible in order to keep these times down. I can remember incidents at previous Pro Tours where a deck check took over 20 minutes, and the match happened to involve players with slow decks; the entire tournament was delayed because of this unfortunate judging incident. When following this philosophy, keep in mind that the overall goal is to have maximum accuracy while still being expedient.
2. Never appear to be biased. Whether you are showing favoritism is irrelevant - the important thing is the appearance of favoritism. Perception is what matters in this situation and judges should do everything in their power to appear neutral towards all players. Whether you have a friend or teammate playing in the tournament or whether you are judging a match involving a notorious "cheater", it is important to never make negative comments about a player and never show a player special treatment. I have seen many judges automatically condemn a player because of their reputation and make comments to the effect of, "I can't wait to give them a warning." This kind of behavior is unprofessional and is just as bad as showing favoritism to a player. At Grand Prix Kansas City one of the table judges in the finals was heard encouraging one of the players who was facing a Pro Tour regular - the judge was basically "helping" the less experienced player feel more confident about the match by commenting about his opponent. Players and judges alike complained about this incident. This type of thing is inappropriate and gives the judge a bad name and hurts the confidence level in judging across the board. Remember - the most important thing is to appear impartial to all players, judges, staff and spectators.
3. Never behave in a manner unbefitting a judge. When you are judging a tournament it is important to remember that you are a representative of the tournament organizer, of the DCI and of Magic. Even though you may be working on a completely volunteer basis and no might have no affiliation with the organizer or with WOTC, you are still going to be regarded as something of an ambassador for the game. Try and take pride in your presentation by setting a good example by staying clean and well-groomed. Remember to wear clothing appropriate to judging when you are on duty (clean judge shirts are obviously the best choice) and do not wear things like team shirts (from any Magic team, regardless of whether team members are competing in the event) and t-shirts with inappropriate material on them. Do not wear your judge shirts when you are not judging an event. Don't litter the playing area, don't use excessive profanity and stay away from silly remarks which could be interpreted as racially or sexually offensive. Although no person is perfect, you can make an effort to develop a pattern of behavior that you would want the players to follow.
4. Never think a job is beneath you. Most judges have no problem saying "yes" to judging the main event of a tournament. When a tournament organizer is running an event, what they really need a good judges for side events and drafts. Although it might seem less glamorous to judge side events, it often requires a judge that is stronger in organization and efficiency than what is required to judge the main event. The worst thing you can say to a tournament organizer that asks you to judge a side event is, "I'm sorry, as a level 3 judge, judging a side event is beneath me." This is the quickest way to develop a bad reputation among organizers and judges. When a tournament is being run, everyone on the judging staff needs to act as a team, there is no room for anything but "team players".
5. Never insult the players. When you are a judge, the players in the tournament should be considered your customers. Your role as a tournament official is to ensure that the tournament operates smoothly and that everyone is treated fairly. A judge should never insult a player, talk down a player or belittle a player in any way. One of the worst offenses I have heard of (which has happened twice over the years) is a judge giving a warning to all of the players in a tournament (because they are talking too loudly and not listening to the judge). This is an example of behavior that insults the players and creates a loss of respect for the judging staff. Other examples I have heard are judges who insult a particular player because of a bad reputation or judges who make comments like, "They are just players, they can wait." This is one of the worst things a certified judge can do.