After establishing the previous year's winners as a baseline, they may judge up to four or five varieties a day keeping meticulous notes on appearance, smell, taste and effect. Some establish a floating baseline with a few favorites, against which all newcomers are compared. Others give each entry equal opportunity.
Effect is the most difficult criterion to judge, especially in a short competition.
Don't start testing before breakfast. Space your samplings with frequent breaks, vigorous exercise, plenty of liquids, and most important, good, healthy food. Start with sativa varieties and end the day with hashish and indicas. Don't muddy your mental palate by mixing in lots of other substances like alcohol, tobacco or caffeine. Steer especially clear of hard drugs.