Pat the area as dry as possible with paper towels or a soft towel. Soak up as much of the spill as you can before it soaks into the couch. Don't rub the area because this will only spread the damage.
Vacuum the area with a wet-dry vacuum to remove even more of the liquid before it can soak too far into the couch.
Spray the area with upholstery cleaner, and pat clean with paper towels or a soft towel.
Remove the cushions from the couch. Open the cushion and take out the foam insert.
Wash the cushion cover in the washing machine on a gentle cycle. Add vinegar if you are removing urine or another heavily-scented liquid. Dry it on low in the dryer.
Soak the foam insert in a mixture of mild detergent and water. Add vinegar for stronger odors, if necessary.
Place the foam insert into the washing machine if it is small enough and run it through the rinse and spin cycles. Avoid using the agitation cycle because this cycle can destroy the foam insert.
Take the foam insert outside if it is too large for the washing machine. Rinse it thoroughly with a garden hose and wring it out as best you can.
Lay the foam insert outside in the sun on a clean blanket. Allow it to dry thoroughly before replacing it in the cushion cover.