[header] How to keep the nose moist to prevent nosebleeds [title] Use a humidifier. [step] You can use either a cool water humidifier or a vaporizer. When the air is very dry, any increase in humidity will help prevent a nosebleed. 
Moistening the air at night will also make it easier to breathe and to sleep. [substeps] If you don't have a commercial humidifier, you can make one by putting a pot of water on the radiator/heating in the winter.