Black condensation mould on walls, ceilings or furniture is the result of a combination of factors: cold surfaces, like an outside wall, high humidity and poor ventilation.
You can prevent condensation by regularly and thoroughly airing bedrooms and bathrooms, heating rooms sufficiently so walls and ceilings retain a moderate temperature and having the ventilation system run for a while after showers or baths, or leaving the window open for about fifteen minutes. Keep the door to other rooms closed to prevent humidity spreading through the property. Regularly remove dust from the air vents in the bathroom or the toilet to ensure their optimal functioning. In the kitchen, always switch on the extractor fan when cooking and keep the fan's filter clean.
We have listed some more tips on how to address condensation mould problems here