When the saddle is new you should apply a thin coating of leather wax or oil. You can use the same kind of appliance that you use for leather boots. When done you should let the saddle soak it in during the night. Polish after 12 hours with a clean cloth. After that you should maintain the saddle twice a year.
Use a saddle cover when using white or light trousers and especially so when riding the bicycle in rain. A leather saddle endures rain but the leather dye can come off then the leather is moist.
A wet saddle must dry by itself or the leather can be ruined. Never leave a saddle cover on a wet saddle.