Every show you judge should be a learning opportunity. Always be fair to the exhibitors, who took the time and trouble to bring their roses to the show. Don't be a judge that only looks for reasons to disqualify a rose. Look for the beauty instead. A good judge will often ask the show committee to move a rose that is misplaced to the proper class if that class hasn't been judged, especially in a local show.
Most shows have a judges' class or two.
Take advantage to keep your exhibiting skills sharpened and enter as often as possible. The best judges are usually those active as exhibitors too. I have noticed that judges often forget, when judging for the court, that they should be looking for the best representative rose of its own variety. Of course, to do this, a judge must see a lot of roses over the course of the growing season. Take the opportunity to visit shows even if you are not judging or exhibiting, and visit gardens in your area.