Weatherstripping is inexpensive and readily available

To prevent drafts, install weatherstripping on windows and doors in your building’s common areas, and in residents’ apartments. Weatherstripping is inexpensive and available at any hardware store. Make sure you get the correct thickness and width for each door or window.  

http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11280