Step one: Go to the dollar store and buy a roll of craft paper for $1.
Step two: Draw out a window scene onto the paper that will fit your window.
Step three: Cut out the scene and tape it up on the window. With the blinds down and the lights on, the window looks awesome from outside.
I put up my Halloween lights just 'cause I'm crazy like that.
One dollar. A buck. And my windows look so spooky I'm scared to come home. Of course, that fear is probably the piles of laundry I know are waiting for me. *shudder*