Most homeowners in Minnesota know it's important to 'winterize' the outside faucets to prevent them from freezing, because freeze damage can destroy the faucet or lead to a burst pipe. The problem is that many people don't quite get it right; winterizing the outside faucets in the fall seems like a simple thing to do, and it seems like it should be straightforward and easy, but there are a few tricks you need to know to really get it right.
Garden hoses - First and foremost, disconnect the garden hose from the outside faucet. If you leave your garden hose attached to the faucet, you're asking for trouble.

Determine if your faucet is frost-free or not. A rule of thumb is that if the faucet has a knob that's perpendicular to the house, it's frost-free. The knob turns a long stem that closes a valve inside the house where it's warm. If the knob is at a 45 degree angle, it's not frost free, and it needs to be winterized. This is only a rule of thumb though; if a boiler drain is installed at the exterior of the home, it will have a knob that's perpendicular to the house, just like a frost free faucet, but it won't be frost free. The photo below shows an example of a boiler drain installed at the exterior of a house.

To know for sure whether a faucet is frost-free or not, look up inside the spout. On a frost-free faucet, all you'll be able to see is a metal stem. On a faucet that isn't frost free, you'll be able to see the valve components open and close when the handle is turned. The images below show a faucet that is not frost-free.

Frost-free sillcocks with an integral vacuum breaker A properly installed frost-free sillcock with an integral vacuum breaker can have the water left on year 'round without any problems. A properly installed frost-free sillcock will have a slight downward pitch; this allows water to drain out when the faucet is shut off.

When frost-free sillcocks aren't installed with this downward pitch, water will sit inside the stem of the sillcock even when it's turned off. The pitch is a little dramatic in the photo below, but you get the point.

If this water freezes, it can burst the stem of the sillcock. Most homeowners don't know this has happened until the first time they use their faucet in the spring. Once they turn their faucet on, water starts shooting out of the burst stem inside the house, making a big mess while nobody is inside the house to see it. This happened to Connecticut home inspector James Quarello while he was inspecting a home a couple of years ago. Better him than me, I say.
The fix for an improperly installed frost-free sillcock is to have it re-installed with a slight downward pitch.