If you do not have EV-only car, open garage door, back up car so exhaust outside (not obstructed by snow pile) if you need to use car to keep warm. Carbon monoxide kills, and has already for those trying to keep warm by running car engine.
Not running car engine, you can use car battery for lights and radio - bring lots of blankets if car is in garage with doors closed, can keep warmish…
Frozen pipe prevention - keep a tap running slow drip - helps internal pipes… Baseboard water heating - make sure to keep all cabinet doors open - and doors - average out remaining heat in house. Close all drapes/curtains… use gaffers/shipping tape to close all gaps in doorways to exterior.
Be careful with interior heating/cooking fuel - do not create excessive carbon monoxide… be sure carbon monoxide detectors work.
So much to consider - but keep safe - best way is to think about what each action you make has.