Condensation can be a big problem in cooler months, and this can lead to mould, which as well as being unsightly can be very bad for your health (the sprores given off can land in your lungs and cause respiratory problems).
Make sure your walls are as well insulated as possible. Keep the place warm and don’t allow the temperature to drop dramatically and turn the heating to low instead of off if nights are very cold.
Keep moisture production to a minimum by closing the kitchen and bathroom doors when cooking or running a bath.
If you’re drying clothes indoors try to leave a window open a little; if you use a tumble drier the door should be well sealed and the drier vented to the outside.