David Stark Design is a book that covers many ideas of decorating different surfaces and walls with Post-it notes. The cool thing about such decorations that you can change the decor of your home temporarily without any damage or clean-up. The good place to start with such decorations is a fridge.
If you want to decorate your fridge with Post-it notes first of all you need to plan the image. A piece of graph paper would help you a lot in that. Each square can represent one Post-it note or a fraction of one Post-It. You just need to draw your image out on the piece of such paper and use it as the guide afterwards.