The question I get asked the most often refers to proper art height. The center of your piece should hang about eye level, which is between 56-60". If you have multiple frames at multiple sizes, cluster them together and determine the middle. That spot should be hung at 56". Always leave 4-8" above a sofa and, like the table chandelier, keep the piece 2/3 the width of the furniture.
Interesting 'rules of the road' for hanging artwork... I'll admit I prefer to just play around with the hanging templates until it feels right... Once that's done (and double-checked with a pocket mirror to make sure it's truly balanced)... Then, I like the idea of checking heights for uniformity (but I just use my nose, shoulder as a guide!)
78 Layouts for Hanging Photographs and Artworks on Empty Walls Like a Pro