Here's a great idea from Stryker on Instructables: Attach your Christmas lights to permanent frames that fit your windows!
The idea is to attach each string of lights so that they are aligned and each bulb is placed just right, then attach them to a wooden frame. Now there's no need to run up and down the ladder, just nail the frame to the outside of the window or attach it with Velcro and the decorating is done!
For another project that can speed up your decorating time, have a look at Stryker's other innovation: Using corrugated plastic strips to hold Christmas lights along the edge of a roof.
(Images via Instructables)