Opt for furniture with legs so that you can see the floor under it. The more floor you can see the larger the room will feel. You can also get some extra storage space under raised furniture, just tuck those baskets and under bed boxes right into the middle so that they can't be seen at eye level.
It sounds obvious but strategically placed mirrors are fantastic for adding depth to a room. Places to target with mirrors are walls opposite windows and doors at the top of stairs.
Colour can also be used to play tricks with your eyes. Light and airy colours tend to move the walls out whilst darker hues will pull the walls inwards.