A standard rule of thumb of when hanging pictures or artwork is to have the center of the picture 57- 60 inches from the floor. This brings the focal point of the picture to eye level for most people. Positioning your central piece according to this rule will make the most appealing presentation.
If hanging a picture over a sofa, don’t leave a lot of wall space between the sofa and picture. Try for 3-6 inches. Any higher will cause the focal point to be the space in between, not the picture.