Leather is a natural material that sometimes comes with varying colors and uneven surfaces. Genuine leather might leave some color when it gets wet. Leather might stretch if you pack your bag too full or load it with heavy items.
Treat your new leather bag with a protector spray that prevents dirt and moisture from soaking into the leather. Moisturize your bag with leather conditioner regularly.
Handle your leather bag with clean hands. If there are greasy stains, wipe the surface with a cotton cloth. Avoid using too much water. Apply a cleaner especially made for leather or soft soap, such as ecological Marseille-soap.
In case your bag gets wet, let it dry away from the sun and then apply moisturizing conditioner. Never rub moist leather, since it might damage its surface.
Stuff your unused bag with bubble wrap or other soft filler to restore and hold its shape. You can store the bag in a natural-fabric bag or inside a cotton pillowcase.