A rule of thumb is to hang all pictures at 5'7" on center. This is eye level to the average human and is considered gallery height.
To do this measure 5'7" from the floor up. Mark here.
You want the picture centered on this height, so measure the picture from to to bottom, then devide that number in half.
Then, subject the difference between the hanging wire and the top of the frame and add that number to the mark at 5'7". That's when you put the picture hanging hook or pin.
It may look low because most people hang their pictures too high, so it will seem odd at first. Don't worry, it's correct!