Check the legs on the piece of furniture. Some types of furniture have adjustable legs that you can manipulate by loosening or tightening a screw. You may see this in metal furniture pieces with slender legs, for instance. Adjust the legs to level the furniture against the floor.
Place a thin, angled item under the "short" leg or side of the furniture. For example, if you are trying to level a chair on a sloped floor, slip a book of matches or a wooden shim under the leg that isn't reaching the ground. If you aren't too concerned about keeping the furniture piece in pristine condition, glue or tape the item to the bottom of the furniture for added stability.
Position a throw rug on the floor and place a shim under the rug. Then place the piece of furniture on top of the rug, directly over the shim so the shorter side is boosted.
Attach furniture levelers to the bottom of the furniture piece. These levelers are generally found in home improvement stores and usually can be screwed into place. Once in place, adjust the leveler to the appropriate height to level the furniture.
Place rubber furniture coasters under one or more legs of a furniture item to add height to specific areas.