When you purchase or inherit a used couch, you also purchase or inherit the stains and soil of the prior owners. Even if the couch in question appears to be unsoiled, it should still be cleaned before using to remove any deep-down dirt that might not be visible. For upholstered couches, you could hire a professional to clean them, but this can be expensive. For leather couches, you could use commercial leather cleaners, but this can also be expensive. Luckily, you can easily clean your used couch yourself at home using everyday products or inexpensive cleaning solutions.
Vacuum the entire couch using an upholstery attachment, which comes standard with most vacuum cleaners. Make sure you get the back, the cushions, the arms, the sides and the skirt. Remove the cushions from the couch and vacuum the underside of the cushions and the seat of the couch.
Attach the crevice tool on your vacuum. Use the tool to clean all the corners and crevices of the couch.
Add steam cleaning solution to your steam cleaner according to the manufacturer's instructions; also add water as indicated. You can use a home model of steam cleaner or you can rent one from your local grocery store. Grocery store models tend to be more powerful and are recommended for heavily-soiled couches.
Clean your couch using the upholstery attachment for your steam cleaner. Start with the removed cushions; pull the trigger to apply the cleaning solution and then run the upholstery attachment over it to remove the moisture. Repeat this process over each of the cushions and then move on to the rest of the couch. For the best results, work in small sections. Add additional cleaning solution and water as necessary.
Allow your couch to dry thoroughly before reassembling.
Vacuum the crevices of the couch the same way you would an upholstered couch.
Mix one part distilled white vinegar with two parts raw linseed oil in a plastic squirt bottle. Shake to combine the liquids.
Apply the mixture to the couch with a clean, dry, lint-free white cloth. Wipe the entire couch down with the moistened rag. Apply additional moisture to the rag as needed using your squirt bottle solution. If the cloth becomes very soiled, switch to a clean rag.
Allow the mixture to dry completely (overnight is best). Use a clean, dry, lint-free white cloth to wipe down the leather and buff it.