It is the connecting point of all the other parts of the building, the unmanifest center of all of the manifest activities. One aspect of right direction involves attention to the sun's relation to the progression of activity in the house through the day. For instance, generally the entrance is in the center of the east wall of the house, the kitchen is in the south east, the dining is in the south. So the sun's life-giving energy enters the house first thing in the morning, proceeds to the kitchen and gives life to the food preparations, and follows to the dining room for the noon meal, which is generally the larger meal of the day for many cultures. And so on, through the house.
Right proportion relates to the overall and relative sizes of building elements.
Certain relations resonate with people better than others. Certainly you have been in a large room with a low ceiling that feels opressive, or a small but high ceilinged room that makes you feel closed in. Take a 3m x 4m room and put an 8m high ceiling, and it feels very different than a room of the same proportions with a 3.5m ceiling. Then there is placement. Obviously all of these work together, and each element has to be designed with each other element in mind.