Do not assume that the other competitors want your 150 pound dog, Moose's mouth all over their 8 pound dog, Teeny's head. This generally works to make quick enemies even though you let them know that your dog is just playing. Do not assume that the other competitors want your long haired, testosteroned male Doberman, Heinz, on top of their champion female Doberman, Perfection, in the ring. Some people just don't want females bred in the ring. Do not assume that Ol' One Eye is perfect except for his one, rather obvious, fault.
Judges consider certain lack of features as being unacceptable for the show ring.
Do not assume that the stuff that Old Smelly should have dropped in the backyard that is still inadvertently hanging under his tail is to be left under his tail. Do not assume that it indicates a healthy digestive system and that the judge will give Old Smelly a ribbon. It is generally not a good idea to force a judge to lift your dog's tail because she feels there might be more than anticipated under there. Do not assume that Frisky has the right to run across the entire set of rings during judging. Some people consider this a distraction.