DID YOU KNOW?
The first decision is where to place your work in the room. Artwork on every wall can be overwhelming. Especially if you are doing an art wall/gallery wall which will likely have many works on it. Adding art on all of the other walls can be visually cluttered when you consider the furniture and other items, such as plants, that are there, too. Museums and galleries are different because they typically lack the furnishings of a home. Artwork on all four walls, especially when displaying a collection of all one type (Impressionists, portraits, works by Monet, etc.) look fantastic when displayed that way.
As a general rule, artwork should be hung at "eye level." That is considered to be 57" - 60" from the floor to the center of the piece including the frame if it has one. To determine where that it, turn your artwork over and find the center from top to bottom. I mark it lightly with a pencil in case I want to move it somewhere else at a later time to avoid re-measuring. I write 60" beside my horizontal line so I will remember what the measurement is for.
If your artwork will hand from a picture wire, pull the wire upward to see how far that wire will stretch when hanging on nails or picture hangers. Artwork should always hang on two nails or picture hangers to make it more secure and so that it will hang straight. The nails should be placed 1/3 of the distance in from either side of the artwork. So, you need the measurement of the width divided by 3 to determine where the nails should go. The wire should be 1/3 or less distance down from the top of the artwork and it should be taut. Wire stretches over time, so periodically check the tension of the wire and tighten it or even change it when it seems to be getting loose.
If you are hanging a grouping of artwork or photos, leave 2" - 4" between edges. Bigger pieces can be hung at a greater distance. You want them to feel like they belong together. Larger pieces of artwork need more space around them. Breathing room, if you will.
The exception to the height rule is when hanging artwork over a piece of furniture. The most common mistake I see is artwork hanging too high. There should be between 6" to 8" between the top of the furniture and the bottom of the artwork, such as over the headboard in a bedroom. In the case of furniture, instead of eye level, the intention is to have the art visually connected to the furniture. Hung too high, it will appear to be floating away.
Another common mistake is hanging a piece or grouping that is too small for the furniture you want to hang it over. If, let's say, you want to hang a painting over a dining room buffet, the artwork should be about 1/3 of the furniture's size. It is OK for the work to be larger, like a 5' painting over a 6' sofa, but it should not be smaller than 1/3 the furniture's size, or in that case, not less than 2' for a single piece or grouping. Try to think of a grouping as one cohesive unit.