Protecting Surfaces
Paint can get on a surface any number of ways -- intentionally or accidentally, from spatters, spills, and drips. When all the cleaning, sanding, and repair work is done, your last preparation step is to make sure to protect any surface you don't want painted.
Protecting surfaces is generally accomplished by masking them off. It takes a bit of time, but it's a lot easier and takes a lot less time than trying to remove paint from a place it doesn't belong -- and from which it may not come off. So don't rush this process.
Painting a room starts with the ceiling, but if you are not painting the walls, you should drape them as shown here. If you are painting the walls, you generally won't have to protect them, even if the wall color will be different than the color of the ceiling. The wall may receive some spatters (minimized by the use of a quality ceiling paint), but you can get at spatters with a quick swipe of a dampened cloth. When masking surfaces, use blue painter's tape. It goes on and comes off more quickly than the old-style masking tape. Remove the tape before the paint dries.