Help - I can never make a light and airy cake!

I'm usually a fairly decent cook but I always fall short in the baking area. Every time I make a cake, it always comes out very dense. I can usually get my cakes to taste good, but they are very heavy. My cakes are never light and airy. I know baking is more of a science than an art so I always follow the recipes to the letter. Am I missing something here? My house is pretty humid, could that be a factor, or is there something i could be doing wrong? A key step that is not typically listed in a recipe? Or is baking just a skill that some (like me) do not have?