1. Balance: Symmetrical balance in interior design is one of the key principle. It means same elements repeated on either side of the central axis.
2. Furniture arrangement: Generally main furniture pieces are placed around focal point. Consider if the furniture is too small or too large for the room. Get rid of it and replace if it's not appropriate for the space. Make sure to balance light and heavy ones as well as high and low pieces.
3. Focal point: Focal points are places that catches eye upon entering the room. Create one if the room doesn't have a natural focal point.
4. Theme: During interior design, house should be considered as a totality of linked spaces. Therefore its best to keep a common theme throughout. It doesn't mean all elements in space is same but they should match each other to create a harmonious space.