Most people have been told many times about the necessity of preparing the surfaces properly before beginning to paint a room. Such preparation involves filling holes and cracks, cleaning off dirt and grime, scraping peeling paint, dulling glossy areas and, if necessary, sealing.

But a professional painter does something else even before he prepares the surfaces. He prepares the room. He protects areas that should not be painted or, more accurately, splattered, according to Andy Lang.Furnishings that can't be protected should be removed from the room. When this is impractical, as with furniture that can't be moved easily, dropcloths are necessary. Nothing should be exposed, even the tiniest bit. Any opening that will allow dust also will allow paint and other particles to come in contact with the furnishings.

Light fixtures should be covered with plastic bags and loose ends sealed. See to it the family does not turn on lights that are covered. Hardware on the walls should be removed if possible, because uninterrupted surfaces are easy to paint, whether you are using a roller or brush or both. Items that can't be removed, such as thermostats, should be protected. Incidentally, you may find a sandwich bag fits right over a thermostat.

Large stationary wall features, such as radiators and kitchen cabinets, once were covered with newspapers that had been pieced together and then attached to the surface. A simpler, neater way is to use masking film rolls that cover large sections of a wall quickly.

Fold them down to protect an area up to 6 feet high. This non-porous material repels most liquids, including paint, and can be rolled or folded easily during a cleanup. It even has "wet paint" imprinted in red lettering to remind everybody that painting is in progress.

You may wish to remove doorknobs, switch and outlet plates, cabinet handles and drapery hardware. Masking tape will protect parts not easily removed, such as door hinges, locks and striker plates. Masking tape also can be used to cover window panes.

Leave an 11-16th-inch gap between the tape and the wood or metal frame, which will prevent contact between the painted frames and tape when it's time to peel away the adhesive. When a surface is exposed to the sunlight for a couple of hours - three at the most - remove the tape. Remember to apply masking tape to clean, dry surfaces. That means making sure the window panes are not covered with condensation.

When masking tape is used to separate two-color work on walls or other vertical surfaces, first paint the top section. When the paint there dries, repeat the process for the lower section.

You also can use masking tape to paint straight stripes on such room features as moldings and chair rails. You should always use a good quality masking tape. It will work well on regular plaster walls and conventional painted gypsum board or other painted wallboard. Do not apply it to wallpaper, unpainted wallboardor acoustical ceiling tile.

Paint manufacturers make recommendations on the subject regarding rubber-base paint, but you are not likely to use it except on concrete, stucco or some other type of masonry outdoors.

It's a good idea, if you are taking more than one day to paint a room, not to stop in the middle of a wall, especially if you have to use a new can of paint the next day. That requires a little planning, which involves deciding on the amount of paint that will be needed for a room and mixing it ahead of time.