When developing a space plan, I always start with a floorplan. If you don't have a floorplan of your room, take some measurements and use graph paper to draw up the room. Looking at a floorplan allows you to get a better feel for the amount of space you are working with, since sometimes ceiling heights, furniture, and other items can make it difficult to perceive space while in the room.
I use AutoCad to create my space plans. Using this software allows me to move furniture virtually before I ever lift a finger in the room itself. With AutoCad I can measure distances for traffic flow, even spacing, and furniture placement. If I don't like it, I simply edit it until I do.