Check the owners manual to ensure that the leather is finished. A finished piece of leather has a glossy sheen and not the rough, natural look of tanned leather. Nearly all leather sofas are finished. If the leather of your sofa is not finished, you must clean it only with an approved leather cleaner--anything else could degrade the color or texture of the leather. If your sofa is finished, it is not necessary to purchase a special cleaner.
Dampen two soft cloths with warm water, wringing out any excess water.
Rub two or three drops of a mild dishwashing liquid into one of the moistened cloths.
Wipe the soiled area with the soapy cloth. Avoid scrubbing, but instead, gently rub the stained area in small circles.
Remove soap residue with the second damp cloth. Rinse out the cloth, if necessary, and wipe until all the soap is gone.
Dry the area with a dry cloth.
Condition the leather with a leather conditioner, following the product's specific instructions. You do not need to condition the leather every time you clean. Using leather conditioner once a year will keep it supple and shiny.