Remember, leather is a natural product and must be fed!
Each bag comes with its own little pot of my homemade intensive leather conditioner, use of which is recommended, sparingly, when the leather feels dry around hard wearing areas such as the bend of a flap and fastenings.
For more general, regular care however I really can't recommend anything better than traditional saddle soap. This blend of oils, mild soap, lanolin and beeswax cleans and softens leather bringing about a natural patina and supple feel over time.
Occasionally, leather with develop and white "bloom". This is perfectly natural and due to the oils in the leather rising to the surface. Buffing with a clean, soft cloth will remove this and along with the above care will keep your bag looking great.