Remove stains from leather prior to cleaning. Apply plain, white toothpaste or aerosol hairspray to the stain. Gently rub into the stain, and wipe clean with a damp rag. For water stains on leather upholstery, rub mayonnaise into the stain. Let it sit on the leather for a couple of hours, and wipe clean with a damp rag.
Tackle mold and mildew on leather upholstery by mixing one part rubbing alcohol and one part water into a spray bottle. Spray the mixture directly onto the mold or mildew stain. Wipe the area with a clean rag and allow it to air dry.
Fill a bucket with water. Add a few squirts of mild dish soap to the bucket. Lather the soap well until suds form in the bucket. Scoop out the suds with a sponge; use only the suds rather than the soapy water. Wipe the leather upholstery gently with the suds and sponge. Get more suds from the bucket and continue wiping down the leather upholstery. Add more dish soap to the water, as needed, to form more suds. Buff the upholstery with a dry cloth.
Combine one part white vinegar and two parts linseed oil into a bowl to use to condition your leather upholstery. You may also use commercial leather conditioners in the same manner. Apply with a lint-free white rag. Use a swirling motion to rub the conditioner into the leather. Allow it to sit on the leather overnight. Buff the next day with a clean rag.