You should first close every thru-hull. Then pour antifreeze into the drain lines such as the galley
sink etc. Do this right now. If the lines freeze and crack the rubber hose they will leak when the temperature rises just a bit. Your boat could sink at the pier. Also, pour anti freeze into the head or drain the water out. A small amount is sufficient, say a half-cup.
Close the thru-hull to your engine. As noted above, the hose can freeze and split. I added a T fitting to the engin raw water
intake on my boat. The T has a length of hose with a bilge
strainer attached. In an emergency
the engine can act as a bilge pump
by pumping out the bilge
. However, this modification is most useful for winterizing the engine. I put the bilge strainer in a bucket of water/antifreeze and start the engine. It sucks the bucket dry in a half a minute or so. Turn the engine off and you are done.
I would also rig a tent from bow to stern with a tarp and some old halyards. That should shed the snow and keep the deck more or less clear.