Here is a handy tool to use on your ladder while hanging your Christmas Lights.  Ladder stabilizers actually serve a couple of purposes.  The first and most important is that it stabilizes the ladder against the house and helps keep it from moving.  Another big one is that it keeps the ladder from leaning against your gutters and causing damage.  They are pretty cheap and can be taken on and off the ladder easily as well.  Hope this helps!  Be careful out there!