what is the best way to prevent condensation in winter?

Plenty of good ventilation. Would be a good start to get double glazing with built in trickle vents. Dont leave damp washing about.

if you can leve a window open

It is very difficult to stop condensation with single glazed windows as the heat on the inside cold on the outside automatically turns any moisture in the air into water on contact with the cold glass good ventilation in cooking and washing areas such as extract fans will help and in addition to those would be double glazing, secondary double glazing would help or a dehumidifier. Also do not leave any wet items of washing around, tumble dryers have to be ventilated properly to outside. hope this helps if so hit the like button Kelvin