For the retinoid - if you haven’t used one before start with Differin! If you’ve done well on that you can go up to prescription tretinoin! I usually sandwich the moisturizer at night - Cerave night cream, Retinoid, then more Cerave for less irritation. For the Vit C serum - store in the box and avoid prolonged exposure to air and light! So I use it, bottle it back up tightly, back in the box & put it away in a drawer. LTKStyleTip LTKBeauty