1. If you aren't able to attend the show but have pre-entered, contact the show secretary to let them know. Don't email them the morning of the show or late the night before. They likely won't be checking their emails as they are very busy. Call them if possible, but be courteous about the time. If you can't reach them, contact a fellow exhibitor and ask them to notify the show secretary when they check in. This allows the show secretary to scratch the entries so as to not hold up the show.
2. If you leave the show early before your breed is judged, again let the show secretary know. Also let other exhibitors in your breed know so that they are aware and can scratch your entries at the table. If you have won Best of Breed and decide to leave before Best in Show is judged, again let the show secretary know.
These tips will help delays from happening in the judging as people search for MIA's. I can't count the number of times we've held up judging and called an exhibitor's name over and over or hunted the showroom in search of them.