A brown or tan stain on your ceiling is probably caused by a leak or excess moisture above the drywall. Water stains will bleed through water-based paint, so they must first be sealed with a stain-blocking primer. Other causes of ceiling stains include mildew, grease accumulation or oil splashes in a kitchen, or smoke stains from candles or cigarettes. Before painting a stained ceiling, you may need to clean it, and you'll certainly have to prime it.
Prepare the area by moving or covering furniture with plastic dust sheets. Protect the floor with painter's dust sheets or builder's rosin paper.
Clean the ceiling stains with warm water and detergent. Water stains, or stains that have soaked into flat ceiling paint, will not clean off.
Prime the stain with tinted shellac-based stain blocking primer. Use an aerosol spray can for smaller stains, or a brush and roller for large stains or to prime the entire ceiling. Allow it to dry. Most stain-blocking primers can be painted over in an hour.
Brush around the edges of the ceiling and around ceiling fixtures with a 2- or 3-inch brush. If you're not painting the walls, apply painter's tape around the top of the wall so you have a straight line.
Roll the ceiling with two coats of latex ceiling paint. Allow it to dry completely before removing the dust sheets so you can be sure you haven't missed a spot. It's easier to see missed spots when the paint is dry.
Locate and repair leaks before repainting the ceiling; otherwise, the stains will return.
Open windows or use fans to dissipate paint fumes, especially when using stain-blocking primer.