Using actual wallpaper is not the greatest idea. Use something like wrapping paper. Obviously wrapping paper is found pretty much everywhere, so thats pretty much the easiest alternative to wallpaper. During study hall or at the beginning of the day, measure your locker. Then measure out the amount of wallpaper you need, then use magnets to attach it to your locker door.
Step 2: Adding Trim Around the Edge of Your Locker
Trim can be anything from feather boas to streamer to strips of fake fur. Measure the perimeter of your locker door, and cut that much of whatever material your using. The easiest way to keep it on your locker door is tape, but if your school has a policy against tape in lockers then you can just use magnets.
Step 3: Magnets
Refrigerator magnets are the greatest and easiest way to decorate your locker. You can make your own by gluing pictures to a piece of magnet, or you can simply buy some magnets. Word and letter magnets are really entertaining when you have extra time and nothing else to do.
Step 4: Scent
Everyone loves a good smelling locker. You can use small air fresheners, body spray, Lysol, Febreeze, but personally I love the little scent balls. They're little balls you place in your shoes or your locker that smell really good. You can find them at most sporting goods stores.
Step 5: Locker Clocks
You should set them to the exact time as your school's clock, so when you go to your locker you know how much time you have to get to your next class. Locker clocks are basically just cheap clocks with magnets stuck to the back of them. This helps especially if the teacher of your next class has a strict policy on punctuality.