fit a fan and ventilate it. If you get the fan to come on every time the light is switched on that will be much better than expecting people to bother turning it on. you could also fit a fan with a humidistat to turn it on automatically when damp but this is more expensive.
http://www.diynot.com/wiki/building:condensation_in_houses
Also identify if it has a damp floor, e.g. if it has no damp proof membrane, or if you have any plumbing or roof leaks.
I see from your previous post that you are in the habit of drying washing inside the house, so it will always be damp until you give up this habit. There is nothing anyone can do to help you prevent damp if you continue to drape wet washing about the house.
A small heater will make it more comfortable but will not remove moisture.