Balance is very important when designing the inside of your house. A lack of balance can show excitement and spontaneity in a room, you need to take into account colour, texture, layout, patterns and many more aspects. Formal balance creastes a mirror image effect and it is also called symmetrical balance. Informal balance uses different objects to create equilibrium in a room. This is much more subtle yet spontaneous and gives a much more casual feeling to the room.
The focus of the room is another important aspect to consider. It is the focal point of the room. Whatever should be the feature of the room needs to have enough emphasis on it so that is does become the focal point of the room. As you walk into the room what you initially take in is the focus. People's eyes shift to the focus immediately and it is the first thing they take in. The focus is generally affected by proximity, colour and the layout of the area.
Subtlety must also be taken into account, how restrained you are has a large effect on the design. Rhythm is another principle that is often looked over, the continuity of the design affects the rhythm. It controls how the eye will move over a room. Repetition is governed by line, colour, texture or form. Progressive rhythm is when the elements gradually increase or decrease in size.
Proportion is another important principle. This includes size, weight and colour. This has a direct affect on the balance of the design as well. Similarly scale is very important. You must effectively measure dimensions of the room and the pieces. The size relationships in a room are defined by these two principles.
You need to consider the harmony of the room. Though closely related to balance harmony is also important. It is essentially how each element of the room works together to be pleasing visually. Harmony encompasses all the other principles and is essentially created or destroyed by successfully juggling all the other elements and getting the right mix.
So if you are looking to design you own house, you must be careful to consider all these principles of interior design. If you are not confident you can always hire an interior designer to help you out, you know you will get professional quality then! However, this can get expensive, and if you want to tackle it yourself, then you now have the right tools! Good luck!