When should I winterize my plumbing, and how do I do it properly?

Winterize before the first freeze, not after. Drain everything: shut off the main water valve, open all faucets, flush toilets, and sponge out remaining water. Disconnect hoses, drain outdoor spigots, and close inside shut-off valves while leaving spigots open. Insulate exposed pipes with foam sleeves—not rags or newspaper—and blow out sprinkler systems with an air compressor. The $50 and few hours of work beats a $2,000 pipe replacement in February.