Paint the ceiling a cool color, such as blue or violet. Cool colors make things look farther away. The ceiling will seem higher, making the whole room look larger.
Choose one neutral color for the entire room. Paint the walls one shade of the color, and the ceiling a lighter shade of the same color. This consistency keeps yours eyes moving without interruption, and your brain will interpret the room as being larger.
Apply a rich, saturated jewel-toned paint to the walls. Paint the trim around the top of the room and the ceiling a clean white. The room will feel as if it goes on vertically right through the ceiling.