I agree on the large mirror thing, although it's meant to be bad for atmospheric and energetic reasons to reflect the natural light back at the window so I would try to angle it so the new reflected light isn't facing directly out the window. also artificial natural lighting can be good! a lovely tall room(Floor) lamp. Wall lights give the long what I image cold feeling of the room some warmth and it won't seem as long and drawn out" A nice corner unit will make the room seem more square! and using a brighter colour on the shorter walls will highlight them and make them appear more even with the other longer walls!! Much like dressing your body for it's shape you dress a room like wise! my English,,,eeek clearly I wasn't concentrated too much writting this! lol