The amulet-jewelry in my online shop is made of raw brass (copper and zinc alloy, (cadmium and nickel free) or 925 silver, without plating. All gems are natural (not produced in a laboratory, nor treated). I intentionally select these kind of materials because they do not involve polluting treatments and are all easily recyclable.
Therefore, to best preserve your jewels, I recommend to:
1) Occasionally remove the oxidation patina that will cover the metal over time, using a microfibre cloth (included in the package) and a few drops of polishing cream for brass or silver (available at supermarkets and specialized shops).
2) Store your jewelry in its original bag or in a box when not in use.
3) Avoid sleeping with your jewelry on and avoid putting it in contact with water and detergents, especially if it includes any gems (some are particularly susceptible to dissolution). The metal will remain intact, but it will oxidize more quickly: you will be able to polish it and return it to its original state, as described in point 1.
4) Avoid playing sports or doing heavy manual work while wearing jewelry.
Treat your amulet jewelry with love and it will love you back!