Wipe with a soft damp cloth {make sure it is damp not wet}
Use a specialised leather bag cleaner for stubborn marks or dirt, but be aware that this can discolour your leather.
Let water drops dry naturally, using heat to dry can warp your leather.
To protect it:
It is worth protecting your leather with one of the many leather protection products on the market. Just remember to test it on a small part of the bag first as it may discolor the leather.
Be aware that unwashed or dark denim may rub off onto the lighter coloured leather if the leather is not protected.
Store it in a cool, dry place with good air ventilation
When not in use, store your leather bag in its specially made dust bag.
Since leather is porous, it loses moisture through evaporation. Use a leather conditioner once in a while to keep your bag super soft, protected and looking its best. Wipe excess product and allow the bag to air dry completely before storing it
Never leave your leather bag exposed to the chemical elements.