A few weeks ago I had the company that installed our irrigation system out to shut it down until spring. There wasn't much to it. The technician that came out ran an air hose from a tow-behind air compressor to a valve under the house and blew air through the lines to clear them out. Had we received a frost while water was present in the lines it could have caused them to crack. I'll have to get the company back out in the spring to open it back up and adjust the sprinkler heads.
With a frost warning scheduled for tomorrow morning I also took a few precautions to keep the pipes underneath the house from freezing. The main thing is closing the crawl space vents. I also ran out to Lowe's this afternoon and picked up two styrofoam covers for the outside spigots. They're on a drawstring that fits over the handle and then tightens to form a seal against the side of the house. At $3/each it's cheap insurance against having to repair a frozen pipe.
Crawlspace vent closed and spigot covered.
The last thing I did this weekend was to adjust the dampers in the attic to change the airflow. Like I referenced in this post from over the summer, in the winter time the downstairs damper needs to be wide open while the two for upstairs upstairs need to be half closed. Since heat rises this directs more airflow downstairs.