Vacuum the leather regularly to remove dirt as it accumulates. Remove cushions as well, cleaning under all sectional cushioning.
Pour enough warm water onto a cloth to dampen it slightly, and wipe over the leather. This will remove built-up dirt and residue.
Smear a layer of toothpaste over any stains on the leather and buff with a damp cloth. The toothpaste will safely buff out the stains without harming the leather.
Create a conditioning treatment by mixing 1 cup of white vinegar and 2 cups of linseed oil. Dip a cloth into the mixture and rub a thin, even layer over the entire sectional. Allow to sit overnight. Buff the sectional the following morning with a clean cloth, using small, circular motions. The leather will become shined and polished.
Apply a layer of stain guard that is safe for use on leather. These can be purchased from any grocery store or home improvement store, and come in either spray-on or rub-on form. This will provide the most protection against stains and spills.