If you have a whole open wall, and no fireplace, furniture, etc to worry about then do the sofa test. Sit in the sofa; see what position is comfortable for your head. To high and you are always looking up. To low...... you see what I am getting at?
A good rule of thumb that I use it the light switch height. I think that if the bottom 1/4 of the TV or bottom 1/3 of the TV is the same as the light switches on the wall, that is normally a good position to do it.
Most electricians use around 54 inches for the light switches.
But that is just my advice. Good Luck!