PREPARE STAINED AND DISCOLORED SURFACES

Water Stains
First, make sure that the source of the stain has been discovered and eliminated. Then:

• Clean as much of the stain as possible with a mild
  detergent and water, then rinse with plain water.
• Allow the surface to dry
• Apply a stain-blocking primer. It can be oil-based,
  alcohol-based or latex. Oil-based and alcohol-based
  are better for tough stains, but require good
  ventilation and an appropriate respirator.
• If you can still see the stain, apply a second
  coat of primer.
• Allow the primer to dry completely, then apply
  the finish coat.

Tobacco, Fire Damage, Soot, Grease
• Clean as much of the stain as possible with a mild
  detergent and water, then rinse with plain water.
• Allow the surface to dry
• Apply a stain-blocking primer. It can be oil-based,
  alcohol-based or latex. Oil-based and alcohol-based
  are better for tough stains, but require good
  ventilation and an appropriate respirator. If there is
  fire damage, an oil-based primer will also minimize
  odor.
• If you can still see the stain, apply a second coat
  of primer.
• Allow the primer to dry completely, then apply
  the finish coat.