Dont use hand cream when carrying your bag, the cream and oils in your hand darken the handles. More so when cream is on your hand they darken faster.
Keep the bag out of the sunlight as much as you can, thats about it. Whether you like it or not its going to happen.
To delay the patina try to carry it on the crook of your arm more than with your hand. Other than that a quick wipe with a baby wipe should help keep it clean.
