In a nutshell, condensation is formed when warm moist air, hits a cold surface, so you've several options available to you:
Reduced the moisture in the air, by either circulating the air (opening the windows), or investing in a dehumidifier. I'd highly recommend a dehumidifier - we've got 2 :)
Make the cold surface, warmer. i.e. invest in some better quality panes of glass such as the Pilkington K glass.
Or you can turn the heating DOWN, as warm air can hold more water vapour than cold air - I wouldn't really recommend this option lol :P