What should I do to prepare my dishwasher if it will be left in an unheated place during winter?

Ask a service technician to cut off electrical power by removing fuses or tripping the circuit breaker, turn off the water supply and disconnect the water inlet line, drain water from the inlet line and water valve, reconnect the water inlet line, remove the plastic sump cover, and use a sponge to soak up water in the rubber boot.