How Should I Decorate??

Ok, So my room has a theme of moons and stars and its taking us a long time to finish it. its from when i was in 3rd grade and i want to make it more "different", i guess. I have a pretty big wall that is completely empty. It has an old window that has drywall behind it from when my parents added an addition onto our house. I was wondering if anyone had a good idea to fill up the wall or what to do with the window? I was thinking big navy and gold stripes, or sections of paintable whiteboard. Also, i don't have a lot of light in my room, so nothing too dark. Any ideas?? THANKS!!!!