the damp micro fiber towel you used to dry it off when ya washed it... each time ya wash it.
Products like armorall don't just make things grasy, they make your leather an armorall junkie.. requiring it to keep from cracking. Keeping it naturally clean is the best thing you can do.
That is what I thought. Haven't had a car/truck with leather in it, so I never had to worry about it. I never use armorall on anything, except the tires if I don't have any other shiny stuff laying around.
I sometimes use Murphys Oil Soap on my seats. I clean houses for a living and have used it on leather sofas and such. Always have great results and never had any problems with it damaging leather, even after long term use.