How can I prevent mold & mildew from getting around my windows & window sill now that the weather is cold?

I noticed that now that the weather is getting colder I can feel the cold coming in & I can see moisture around my windows. Last year I didn't notice this right away because my bed is right by the window, but when I moved it I saw mold & mildew all around the window & wall. How can I prevent this from happening this year?