Sometimes this is due to driver error.
If your car does not start try these tips:
1. Turn off your radio, heater, lights and any other accessories in the vehicle to allow the car to pull more power from the battery to start.
2. Run the engine for two minutes before attempting to drive the car. Start out slowly on your journey and do not accelerate quickly until the engine warms up.
If it is not driver error you could need a new battery and/or new glow plugs. Both are fast moving parts at this time of year. We can advise you on whether they are necessary or not, and fit them if they are.