The order in which you apply your skin care products affects the way they work. To get the best results, remember to start with the thinnest and finish with the thickest products. Your serums go first, then your moisturizers, next is any spot treatments, and next your SPF primers. Confused about applying Vitamin C and Retinol? Vitamin C is best in the morning (orange juice) and Retinol at night (Vitamin A = asleep). A good skin care regimen is your foundation to healthy skin.