Lemon is one of the best natural bleaching agents and one can feel the difference after first use. Just squeeze a lemon and apply its juice directly on the skin or you may add other natural ingredients such as glycerin or honey or curd to make it slightly less acidic.
Use this pack once a week. Make sure you avoid the area around the eyes and do not go out in direct sunlight after applying this packs. Follow it up with a good moisturising sunscreen to protect your skin.