There's a great post at the "Miles and Emma" blog with some tips and suggested etiquette for "fun matches," a slightly-more-formal event than our run-thrus, but not a trial. This is a great list for people new to agility, run-thrus, and trialing, and a nice reminder of good manners for those of us who may have become too comfortable and cavalier about our weekly run-thrus (I apologize to EVERYONE for violating #10--often.)
http://www.milesandemma.com/
While this is directed at participation in fun-matches, these are all good-practice for actual trials, too, because even though it may look like this:
https://www.flickr.com/photos/lcdapics/8069080009/in/set-72157631725481832
we really want all of our agility events to run as smoothly as possible!
