That is a huge question because there is so much to consider!! I will address some of the most important ones here.
First of all, consider the site. Does the house fit the site well? Can it be situated so that it is open in front? It is important to have some protection in back and on the sides, preferably with the land in back higher than the land in front. The idea is to feel as though you are in a big armchair.
Water is best in front of the house. This goes along with the land sloping gently down in front of the house. Water rushing right toward the house would not be positive.
Be sure your entrance will be clearly seen as you approach the house. What you first see most affects your chi! In order for a house to be welcoming, it is important that the way into the house is obvious. A defined meandering path should lead the eye and people to your front door. Also consider whether or not the house is designed so that you will use the front door. It is the mouth of chi, so it is important for you, the homeowners, to use that door. Too often, houses are designed so that the people who live in the house never use the front door.
I like to look at the shape of the house, including attached garages, decks, etc. A house does not have to be square or rectangular, but it is important to get a sense of a complete shape after landscaping is done. The more complete the shape, the more supportive the space will be.
Next consider the ceiling height. Ceilings that are too high make a space feel too yang, whereas ceilings that are too low can make a space feel too yin and confining. Beams are also a factor. If you are building a house with beams, it is best to have them a little higher than a normal ceiling so they will not impact the chi of the space as much.
Avoid the rushing chi of long straight hallways, front doors opposite back doors, and stairs opposite front doors. In these situations, the chi will rush right through the space and not stop to nourish those who live there.
Figure out where the furniture will go. Be sure that the beds, couch, desk, and stove are all in the command position. That means that when you are in/at any of these pieces of furniture you can see (are facing) the door, but are not in direct line with it. Many stoves in new houses have microwaves above them that serve as mirrors so that it is possible to see behind you as you cook. This compensates for not having the stove face the door.
Plan open spaces so that there is a way to define different areas. Also be clear about what each room is for. This does not mean that a room cannot serve dual purposes. It does mean that it is important to be clear about what those purposes are and that they are compatible.
Take a mental walk through the space and check for flow of movement. Too many doors in one area can create a lot of arguments. Are there sharp corners? Is it easy to get one from one place to another?
Storage is extremely important. Plan for useful and accessible storage that is in keeping with the number of people who will be living in the house. Do not, however, take anything with you to the new house that you do not love or use. This is the perfect time to start clearing out the clutter in your existing space.