The way I do it in my house is to put my arm straight out in front of me and touch the wall with the tip of my finger. That's where the center will be.
I'm 6 ft. tall. If I put it at my eye level, everybody hates it. Putting it at my shoulder height seems to be comfortable for most people.
The only time I put things higher is when it is a large room where people are likely to view from a distance. Then I put things head high.
If I have a group of pictures, I place the center of the group at my shoulder height.