The single most reliable indicator that a room was decorated by an amateur is art hung at the wrong height.
The Centerline Rule
Art should be hung so its center is at 57 to 60 inches from the floor. For rooms where people are primarily seated, hanging art slightly lower — around 55 to 57 inches — often looks more balanced.
Art Above Furniture
When art hangs above furniture, the bottom of the frame should be 6 to 10 inches above the furniture top edge. The width of the art should be 50% to 75% of the furniture below.