To clean your leather product, rub lightly with soft damp cloth dipped in a light shampoo solution.
Keep your leather bag well aired out, or in a cloth bag. Do not close in plastic bags for long period of time,
Use the storage/travel bag the item came with, or some type of BREATHABLE fabric like pillowcases.
If your bag gets wet somehow, you should stuff it and let it retain shape and leave it to dry in normal light. Do not dry in direct sunlight or with a hair dryer. It will become stiff and cracks may develop.
Rub a leather conditioner into the leather product once every quarter.
Remember Oil and ball point marks are the worst enemies of leather. They will never come out.