I saw this list of wonderful hints in one of my favorite on line mags - Adore. I think they really make a lot of sense and take all of the guess work out of pulling a room together. The hints are simple but effective as you can see by this picture.
Match at least one cushion on the bed/sofa with a rug or carpet in the room.
Connect the colours of the cushions, accent chairs, and lamps with those of the drapes or window treatments to maintain the theme.
Bring in pops of colour with smaller objects while letting the larger pieces of furniture and the walls be a neutral foundation.
Be sure that any colour you see in the foreground is connected on the other side of the room.