The very first thing to do is to clear out the room and give it a thorough cleaning. The cobwebs and dust will all have to go. The job can be done quickly with a powerful vacuum cleaner. Otherwise a good old-fashioned broom will have to suffice.
Next, any repairs, minor or major, that are necessary have to be carried out. It is no point doing up a room with broken window panes, gaping holes in the ceiling or a cracked floor. Such things have to be attended to before any brightening up can even be started.
Assuming that the room is now in decent condition, the next thing to do is to pain the walls and ceiling with cool attractive colors. The choice of colors is very much up to whoever uses the room, but I personally prefer a light cool blue for the walls and white for the ceiling. Too dark a color makes the room look gloomy and too bright a color makes the room not restful. Light blue or green are usually most suitable.
After painting, the room will certainly look a thousand times better than it was. Color has an effect on us, so say the psychologists. This is certainly true. I am sure no one would like to be in a room that is painted black. Anyway no sane person would use black for his room.
Next the windows need to have curtains or blinds. This depends on what the room is used for. I will take the case of a bedroom. Colorful curtains hung on both sides of each window will do nicely. Again the colors for the curtains should not be too dark.
The furniture in the room has to be considered now. For a bedroom, the necessary things are a bed, dressing table, table lamp and wardrobe. There is no hard and fast rule on how they should be arranged, but the arrangement should be both functional and comfortable. Also it is important not to clutter up the room with unnecessary things.
A bedroom is better lit with soft incandescent lamps of forty or sixty watts. Fluorescent lights tend to be a bit harsh and is more suitable in an office. Preferably the lights should be shaded to give it an even softer effect. A bedroom is supposed to be a relaxing place, so the softer the lighting, the better it is.
Finally a framed picture of a natural scene will do wonders for the room. It will give the room a feeling of airiness and comfort. Speaking of comfort, it is not compulsory to have an air-conditioner for the room. A good ceiling fan will do just as well.
So with the above successfully done, the room will certainly not be drab. It will be a comfortable and lovely place to be in.