Ambient light sets the overall level. Task light helps you do something: chop, read, apply make-up. Accent light draws attention to art, texture or architecture. Rooms feel flat when they rely on a single ceiling fixture.
In living rooms, aim for at least three light sources at different heights. In kitchens, under-cabinet strips do more for usability than extra downlights. In bedrooms, put bedside lights on separate switches so one person can read while the other sleeps.
Choose warm colour temperatures (around 2700 to 3000K) for living spaces and specify dimmers wherever possible. They are the cheapest way to change the mood of a room.