If it's genuine leather, it shouldn't deteriorate the way the fake stuff does (in other words, quickly and simply by existing).
Dust it regularly and avoid direct sunlight, excessive temperatures and humidity levels (high or low). Basic stuff for any collectible. Beyond that, you might condition it once or twice a year to keep it soft and supple (as opposed to crispy). I don't know how necessary that will be for this, but it's standard practice for other leather goods. Maybe Prime 1 will mention something in their instructions. But probably not.
Hot Toys - Joker - 1/6th scale The Joker Collectible Figure
