Color coordination and lighting (fancy lights as well) 

For me it's the colour scheme and the proper arrangement of the furniture with similar design and colour to the room. Colour used in rooms shows our mood and thoughts. Avoiding dull and too bright colours is the best option.

For me it is light and lightening: No matter how many artificial lights you use in a room, it can be as good as natural light. So, always look out for option to have maximum natural light in the room. The doors and windows of a room should bring in as much daylight as it is possible.