First, It's about drafts, those annoying little air flows that make a home less comfortable AND make it cost more to heat and cool. Your energy audit, whether professional or done by you, should include a list of those drafts. Plugging them is your first line of energy defense.
Seal the Leaks!
Caulk, foam sealant and weather stripping are your first line of defense against air leaks. If you've never used these tools, here are some simple "how to" videos that'll show you, well, how to ...