Before choosing a sofa, list what really happens in the room: conversation, television, reading, children playing, guests staying late. Each activity needs its own zone, and the busiest one gets the best light and the most space.
Keep clear walkways of roughly 90 cm through the room, and around 45 cm between the sofa and coffee table: close enough to reach a cup, far enough to move past. Float furniture away from the walls where you can; it makes a room feel more generous, not less.
Finally, decide on one focal point (a window, fireplace, artwork or the view) and orient the main seating towards it. The television can live on a secondary wall or be concealed in joinery.