This is such an important question. You likely already have art at home that has a place on your wall, so what do you do when a new piece arrives?
Let's begin at the beginning. You have received a new piece and you have a lovely wall space for just that piece. Easy. The ideal height for hanging art is 58" to the centre of the piece. This puts it at the average eye level. The problem with this new knowledge is that you have to calculate a few measurements to actually arrive at the centre of your piece hanging at 58". It's necessary to factor in the apex of the wire hanger on the back and how far it sits below the top of the painting. Once you know the apex, calculate how far that is below the edge of the frame. Mark that measurement down. Then measure the height of the art work and divide that in half. Then subtract the distance between the wire and the top of the frame. Put the nail at that height.
Now what if you have several images that you want to arrange on one wall. I found a wonderful article that talks about laying out your images in a Salon Style. I'll include the link here for you to visit that article.
I found the illustrations to be really useful. The article also includes some guidelines around colour choices. If you have too little colour or too much colour how do you handle that. What if you have modern pieces and traditional pieces, how do you handle that? Very interesting.