Lexol cleaner and conditioner. Wash it with the cleaner (sudsy and wet), rinse it well, quickly blot up the excess water, then apply lots of conditioner and let it sit overnight. At the leather dries, it will pull the conditioner in. Also be sure you remove the grainy stuff from the seams, as this stuff will tend to wear out the leather there, causing splits and tears.
I've done this with many leather products (motorcycle jackets, hephalump boots, the leather in my truck) and they are all holding up well. The elephant skin boots still look good after 17 years.
The leather in my truck has a few blemishes, far less that one might expect after 5. 5 years being outside and 137K miles. Cleaning and conditioning with Lexol has made a significant difference. I haven't cleaned it much more than every year or so.
Fest3er