A few hours of planning can save a lot of time and trouble down the road. There are many programs around that let you map out your room and electronically move around the furniture. This saves not only time but often a trip to the ER for a pulled muscle.
For those more prone to a low-tech approach draw a floor plan of your room on a piece of paper and cut out smaller pieces to represent the furniture and your equipment. Know the limitations of your room and plan accordingly. For example, a bright, sunny room with many windows may not be the best place for a projection TV. If it is the only room that is feasible, perhaps drapes, blinds or shutters can be used.