Fix air leaks in your home with starting with your doors. Check your front and back doors for space underneath them. Peek down there, and if you feel air coming in, then there are air leaks in those areas. Another method of checking air leaks is to do it at night-time. Ask the help of someone else from your family, and have him use a flashlight from the inside while you’re outside to observe. Tell him to point the flashlight along the edges of door-frames and if you see a lot of light seeping through in some areas, then there are air leaks there.
Move on to your windows. Check if there are gaps in the windowsills. Most people suggest using a candle to test windows. Hold the window near the windowsill and see if it flickers. If it does, then there's an air leak. If there are air leaks and you can't afford to replace the windows just yet, you can use electric tape to cover the space. Foam liners are also good alternatives. Proper insulation however, is strongly recommended, as they will keep air leaks from happening again for a longer time. Check also for cracked windowpanes and replace them right away, if there are any.
Check your walls, especially the outer ones. There may be unnoticed holes and cracks where air drafts can come in. Remember that there is no crevice small enough, all of them should be found and properly covered up. Electrical outlets can be one of the worst air leaks, so better check them out, too.