Ask friends if they have any leftover white paint and paint your wooden furniture.Use old clothes to cover cushions & lampshades.Declutter anything dark or not used.Display only light or clear glass things. Put your mirrors opposite windows to reflect light.Light coloured sheets can be sewn onto existing dark curtains,even if it's only the middle section. Tell your friends what you are trying to achieve , they might donate things, keep everything clean and smelling nice