This is what you need to do. It's very similar to what you'd do with an RV.
First, turn the water off at the city meter at the street. The pipes that run under ground are safe. They are buried below the freeze zone of the ground. That is required by code.
Next, blow your water lines with air, like you'd do with your RV. How?
You attach an air valve on an outside faucet and attach that to an air compressor. Turn on the air compressor and then start draining water from each faucet, hot and cold.
Now, water will be under pressure in your water heater when using an air compressor. That is, until the water at the top of the water heater is displaced with air. Once it's displaced with air, no more water will flow from the water heater. The "out" line is at the very top of the water heater.
Keep blowing air with the compressor. The hot water lines that still have water in them will purge out. Once they start spitting with air, you know the lines are clear.
Just like in your RV, do one faucet at a time, hot and cold, until each spits air.
When everything is done, THEN finish by draining the water heater. If you want the water heater to drain faster, you can continue running the air compressor, keeping some pressure on it until empty. (or turn the compressor off and let gravity drain it, it's slower though).
Some snowbirds I know go one step further and actually winterize the house water lines with RV antifreeze by pumping it with an external pump through the outside water spigot. Some also do some creative plumbing and put a water by-pass on their water heater so they can winterize the lines in the house with out putting antifreeze in the water heater. They simply drain the water heater, exactly like you'd do in your RV.
Now.... here's something you REALLY need to consider.... the actual walls inside your home.
This actually happened to my mother's house. One year she decided to visit my sister in Texas. She lived in central Indiana. She was with my sister for about 5 months over the winter. Before leaving, she lowered the thermostat for the furnace as low as it would go, just barely enough to keep the house and pipes from freezing .... like ... 33 degrees.
After 5 months and temps in Indiana that reached (real temperature -20... yes, 20 below zero) and a horrible cold winter, yes the furnace maintained the heat, BUT the plastered walls could not tolerate the cold.
Her walls were true plaster. NOT plaster board. And there were several places where the plaster crumbled. She had to have several places fixed, and yes, I did most of it.
So, that is a word of caution if your house is in a freeze zone and you plan on shutting down all heat. What effect with extreme cold have on the rest of the house. Plumbing may be safe, but what about everything else?
Anyway, that's how it's done.
This is what you need for the outside spigot. Clip the air compressor hose directly on the end.
Click here.