Color and personal items make a room. A fun piece that you treasure can be the personality of a room.
A few tips:
Arrange the furniture to form a more intimate seating arrangement. Furnishing do not always have to be on a wall. They can float in a room forming a great conversation circle.
Add something large like a serving tray to a coffee table that you can put smaller pieces into. This helps to ground the space and make it feel less cluttered.
Draw color and inspiration from pieces that you already have in the room. This helps to give the room a more unified feel and makes the space flow.