First, try to familiarize yourself with the event as much as possible if you are a newcomer. Many LD judges do not have prior experience with the event or with LD. Reading this guide is a good start. You also may want to search for LD debates on YouTube to get a sense of some (slower) LD debate rounds.
Second, make sure to judge based on the arguments presented, not on your own convictions. While many LD topics are controversial political and philosophical questions that you may have an opinion on, debate is for the debaters. Vote for the better defended argument, not who made the argument you agreed with.
Third, make sure to take careful notes. This is known as “flowing.” Debate is often about technical refutation, and an argument not addressed is seen as “dropped,” or true. Arguments not previously addressed cannot be addressed new in a final speech. Take careful notes to make sure you can see who answered what argument.
Fourth, produce a judging “paradigm” or a set of guidelines about how you judge debates. This is put on Tabroom, where competitors can see a list of judges for a tournament. You should be candid about what you like to see in a given round.