Plus, tire pressures drop. So check and make sure they aren't low. Use a gauge, eyeballing doesn't work. By the time a modern tire looks low it is nearly flat. The TPMS will pick a low tire up before it looks low, but they have a wide enough range to not report a tire that is slightly low.
Use the front defroster only when needed. The AC compressor will run even though the AC button is not on.
That's only partly true. The AC low pressure switch will keep the compressor from running when the temperatures get down near freezing. The temperatures vary with the unit, but usually about 40F or 5C will be the cutoff. The idea is to keep the evaporator from freezing up.
Of course, if the compressor DOES run it provides a bit more load on the engine, which will then warm up more quickly.
Leaving the heater blower off until the engine warms does help the engine warm more quickly. In truly cold weather there is a hazard involved in leaving that motor off. If the defroster is turned on after the engine warms, the blast of hot air hitting the cold windshield has been known to crack the glass. Decades ago Americans stationed in Alaska were told to turn the defroster on as soon as they started the car, to avoid that very problem.