Check for Gaps in Windows & Doors
Weather stripping is relatively easy and available at your local home improvement store. Stop drafts from coming in and heat from leaking out of your home through drafty doors and windows.
Use caulk to seal gaps in the walls of your home or apartment. Wherever different building materials meet, or wiring comes out of a wall, there are gaps that may contribute to the loss of heat in your home.
If you have older or leaky windows, consider temporary fixes, such as plastic film kits that create the effect of an interior storm window.