Consider the scale and proportion of your main pieces as they relate to the size of your room. If all the "heavy" furniture is on one side of the room, it will feel lopsided. Likewise, if furniture hugs the walls and is too scattered, the room will lack intimacy.
Mix things up by using furniture with varying heights and depths. In proper combination, this contrast creates balance and interest.
In a larger room, try creating a combination of conversation areas and/or activity areas such as a small table and chairs for a child's drawing station, or a tall table and barstools in front of a window for a quiet cup of coffee.