easiest way to clean leather sofa?

Hoover the cracks first with the brush attachment, crumbs act like sandpaper. Then a microfibre cloth barely damp with water and a drop of mild soap, wipe a section, dry it straight away with a second cloth. Leather does not like being wet. Every few months a leather conditioner keeps it from drying and cracking. Skip anything with vinegar or ammonia, and try whatever you use under a cushion first.