The best way to decorate shelves for Christmas is to add some festive elements that will make the space feel more like the holiday season. Some ideas include hanging garlands, adding holiday-themed books or ornaments, placing small Christmas trees on the shelves, and hanging stockings or other decorations. You can also add lights or candles to create a cozy and inviting atmosphere. Additionally, you can add some Christmas-themed trinkets or knick-knacks to add a bit of whimsy to the space.