There are a lot of ways to create an interesting mantle depending on the layout and style of your room. The key to it all …is the layering of objects. On this mantle the bird and butterfly prints are the center large focal point. This center focal point can be a mirror, artwork, even a TV but whatever the object is, it will serve as the anchor for the remainder of your design and should be the tallest object in your overall design. Also, ensure that its scale is appropriate for the space. The visual weight of this object should adequately balance out the visual weight of the firebox below the mantel and should fill a large portion of the wall above the mantel.
In this photo the moss orbs and candles on either side creating symmetry while the vase and branch complement the vase with leaves as well as the branch of driftwood. The branch also creates some visual weight and height. The driftwood branch helps create movement on the mantle. Choose objects for the right and left sides of the center piece that will add width and visual weight to the overall design. These items do not necessarily need to be identical, so long as their visual weight is similar. When choosing these items, make sure that their height is smaller than that of your center object but still proportionate.
Add objects of varying heights to the center of the mantel underneath the focal point. Varying the heights of these objects is important so that you do not to create any horizontal lines with your design which would then detract from the horizontal line of the mantel itself. You do not want anything to compete with the mantel! Again, as you choose these items, keep their scale in mind to make sure they are smaller than the items chosen for sides but still proportionate. If you want a very clean, minimal design, you might opt to skip the last layer.