Vacuum the cushion to eliminate any crumbs, dust or loose debris.
Spray the outside of the cushion with white vinegar from a spray bottle to help remove any stains that have developed on the fabric.
Use an iron to apply a cloth repair patch over any threadbare or worn sections of cushion to help restore the function and appearance of the exterior. The patch should be as close to the color of the cushion as possible so the repair isn't as noticeable.
Unzip the couch cushion and either replace the stuffing with a fresh batch from a furniture store or add some more on top of the existing supply to restore your cushion's firmness. Natural cotton filling works well for this, as does foam.
Place a slipcover over the cushion if it still doesn't look the way you want it to. Slipcovers allow you to freshen up the cushion's appearance by altering its color while providing an additional level of protection against damage.
Place fiberboard under the cushions to further increase their firmness. This is especially useful if the undercarriage or frame of the couch has weakened with age.