Ideally, you should take your car out during the winter to keep things moving and prevent tyre flat spots. Before you lay it up, make sure all the fluid levels are topped up - especially the coolant. While you may not be using the car, it's important to help prevent corrosion. You could also invest in a trickle charger to keep the battery in good nick. Don't leave the handbrake on otherwise the brakes will seize. You could also consider using an additive in the fuel tank to stop the fuel 'going off'. Modern fuels contain ethanol, which can be harmful to many a classic's components - the damage is done when the car is not used and the ethanol starts to become separated.