Most winter breakdowns come from a small number of causes, and most are preventable with a check before the cold arrives.
The battery
The largest single cause of winter breakdowns. Cold reduces available capacity while the engine needs more current to start.
A battery more than four or five years old is a reasonable candidate for replacement before winter rather than during it. Many garages test them free.
Tyres
Tread depth matters more in wet and cold than in dry. The legal minimum is well below what performs adequately in poor conditions.
Winter tyres use a compound that stays flexible below about seven degrees, which improves grip substantially even without snow. In regions with real winters they are worth having and in some countries mandatory.
Fluids
Screenwash at a concentration rated for the temperatures you get. Frozen screenwash in the reservoir is common and leaves you unable to clear salt spray.
Coolant concentration, which protects against freezing and against corrosion.
Visibility
Wiper blades, which perish and smear. All lights working, checked with someone watching.
What to carry
An ice scraper, which sounds obvious and is frequently absent. A blanket, a torch, a phone power bank, and something to eat if you drive rural routes.
Jump leads or a portable jump pack.
The driving part
Clear the whole windscreen and roof, not a small patch. Increase following distance substantially. Brake and steer gently.
And on ice, everything happens slower – inputs and reactions both.