Blot the stain immediately with a clean cloth or paper towel
Use cold water only
Mix a small amount of mild liquid detergent with cold water
Dab the stain with the solution using a clean cloth
Blot with a dry cloth to lift moisture
Apply a paste of baking soda and cold water if needed
Let the paste sit briefly, then blot it away
Use 3% hydrogen peroxide on light-colored mattresses if the stain remains
Dab gently and blot as the blood lifts
Repeat as needed with fresh cloths
Avoid hot water
Avoid rubbing the stain
Let the mattress air dry completely
Use a fan to speed drying if needed