I tend to place items along the walls of my rooms, leaving the middle sparse. Especially the main room where I feel I'm blocking off the doors. In my kitchen I find an island works nicely. In the living room, maybe a low table with some cushions for seats. Any other ideas?
I usually make little zones in each room. Carpets really help with this since they make a good border for an area. This helps me fill in the center area instead of putting everything against the walls.