Leather is a living material that evolves over time. It is therefore very important to take care of it so that it lasts longer.
Do not store your bag wet or dirty, clean it first, and protect it with a cloth cover.
To clean your leather bag without the risk of damaging it, use commercially available cleaning products, or use talcum powder. Sprinkle your bag with talcum powder and then wipe off the paste with a soft cloth or cotton ball. Your bag will then regain its natural shine.
Another tip from grandma, especially effective for shining leather. Wipe it with the inside of a banana peel.