One of the more well-known ways to decorate a mantel is to implement the "three-plus-one" trick. This design technique relies on layering objects of different heights to create visual interest. Find three similar objects and place them on one side of your mantel. Try not to line them up — layer and stagger them. Play around to find what looks and feels best for you. Once you've done that, find one larger object and place it on the other side of the mantel. The general rule is that this object should be at least twice as large as the other three, but this doesn't need to be exact. Try to have a unifying element for all of these objects — whether it's color, texture or a theme.