Use often and wash when needed. Hand-wash in cold water, use a dark formula laundry detergent, and air dry. The denim will lose a bit of the indigo as it ages and washed. The leather might pick up some of the indigo when it is washed. Condition the leather as needed.
Raw Indigo denim has a tendency to crock, this is a process where the Indigo dye rubs off. Avoid rubbing up against light colored clothing and upholstery.