Your bike will work best if you keep it clean. In the past few years, most municipalities have started treating the roads with a slurry mix that is applied either from a sprayer truck or mixed with the rock salt they spread.  This stuff will ruin your bicycle.  Bicycle frames and components will rust or corrode incredibly fast.  If you’ve been riding when the roads are being treated, you’ve got to clean your bike afterward.  While there are a lot of products out there for cleaning bicycles, you don’t need the fancy stuff.  I use Blue Dawn and hot water.  Mix about 1 inch in an old spray bottle with hot water, spray your bike liberally, wipe it down, and rinse with plain water.  Microfiber clothes work best to dry them quickly and re-lube as needed with the water-repelling lubricant.

With the exception of most “Fat Tire” bikes, you really shouldn’t be riding on the same tires year-round.  Most high-performance tires tend to be constructed with fairly light carcass / thin sidewalls, which are great for summer because they offer great grip and allow greater speed. (who doesn’t want to go faster) Winter-specific tires are usually heavier, have thicker carcasses all around, have deeper/more significant tread patterns, and are sometimes studded.  It is really up to you whether your wheels are tubeless vs tubed if your wheels are so equipped.  My suggestion is to go tubed.  Tubeless takes way too long to repair on the side of a trail.

Slippery conditions require that your brakes work correctly. A sticking or sluggish system can often cause an unexpected loss of control, usually caused by a locked-up or skidding wheel.  Rim brakes are the most susceptible, but disc systems can also be compromised in winter riding.  Frequent cleaning of rims/discs and pads will prevent problems.  Lubricating the cables with a dry lubricant will help repel water and corrosion, ensuring smooth operation.  Hydraulic systems usually don’t have issues until very extreme cold temperatures, but keep an eye on your lines; cold reduces their flexibility, which can cause leaks.

Fenders will help keep your bike clean & keep you dry

Install the brightest/best you can afford.  Headlights should be installed on the bike and helmet; I usually use at least two taillights.

Winter riding requires lubrication different from summer riding. Summer lubricants are often thinner and lighter, intended to repel dirt and grime, which often causes premature component wear.  Winter lubes are heavier and intended to stay “wet” to repel water, mud, salt, and other corrosives that you encounter.  Too much of either is never a good thing, but summer formulas usually get washed off too quickly.

If at all possible, store your bicycle indoors in a heated space.