Take your mattress off of the bed and situate it in a spot away from furniture and walls so that you can easily access both sides. Vacuum both sides of the mattress thoroughly with an upholstery attachment on your vacuum cleaner.
Fill a bucket with 1 quart cold water. Add 1 tablespoon. laundry detergent. Use a hand whisk to mix up the soap and water to create thick suds.
Dip a sponge into the bucket to scoop out the suds. Scrub any soiled or stained areas on both sides of the mattress. Use a circular motion when scrubbing and apply more suds as necessary until the stain is gone.
Clean the entire mattress with upholstery shampoo. Follow the manufacturer's instructions for using the upholstery shampoo as this will vary among products. Allow the mattress to completely dry after cleaning with the upholstery shampoo.
Sprinkle baking soda over the entire mattress once it has dried. Let it sit on one side for about ten minutes, vacuum it up, then flip over the mattress and repeat on the other side. The baking soda will help to freshen up the mattress and remove any odors.