how to place art pieces

Hi art or design experts,

How do you place art pieces around the house? Can advise please?

From what I know, you have to measure the item you intend to place it above and cater at least 2/3, about 8-10 inches above say the sofa, at least 60 inches from the floor and give about 2-5inch between each frame. However for simplicity's sake, say for example a 3-seater sofa, a dining area (for a standard 1.5m table with 6 chairs), a standard king/queen size bed, what size art pieces will you cater above these furniture pieces?

For sofa, will 3 pieces 50cm x 70cm or 2 pieces 60cm x 60cm work?

For dining area, will 3 pieces 50-70cm work?

For king/queen bed, will 2 pieces 50-70cm work?

Thanks!