Always run your vented Range Hood every time you cook so that you eliminate Steam, Smoke, & Food Particles that get into the air that can create problems. Stream and cooking in general will create moisture which can breed mold. Also it can help eliminate particulates in the air that could have an effect on people that have asthma or other breathing issues not to mention the dirt/germs that can build up from these particulates overtime.
Never Warm up your Car in the Garage with the garage doors closed or even if you have the garage doors open. Carbon Monoxide is a very dangerous gas that can still collect in a confined area and even with the doors open still will collect and takes time to dissipate and most people will close the garage door when leaving and can trap the residual Carbon Monoxide in the garage and can eventually work its way into the home.
Wait until Spring time to Paint, have Carpets Cleaned, and even buy New Furniture. As all of these have chemicals that emit by evaporation into the air and you want to be able to ventilate your home which you cannot or would not want to do in the winter time.
Always turn on your Exhaust Fan in the Bath especially when taking a shower or running water which will create moisture in the room and most people keep the bathroom door closed which traps the moisture in the room which eventually could lead to mold growth.