A clean leather couch makes a bigger difference than you'd think. Here's the most effective method, plus the mistakes most people make.
Vacuum the entire couch with a soft brush attachment to remove dust, crumbs, and pet hair.
Mix a few drops of mild dish soap with distilled water in a bowl. Test on a hidden area first.
Dampen a microfiber cloth with the solution, wring well, and wipe the leather in long strokes. Do not soak.
Wipe the leather dry with a clean microfiber cloth. Do not let the leather air dry as it can leave water spots.
Apply a leather conditioner with a clean cloth. Rub in circular motions and buff to a soft sheen. Conditioner prevents drying and cracking.