As a rule of thumb products should be applied from lightest or thinnest to heaviest or thickest. Always start with a clean slate aka face. If your cleanser is not pH neutral, use a toner to set it back to a neutral pH. Next consider a serum - usually packed with goodness for your skin such as vitamins, antioxidants, hydration. A lotion or cream should add moisture and protection to your skin and seal in hydration. Alternatively, a face oil may do that job (depending on your skin type and needs). Lastly: sun protection. Allow for each product to soak in before you add the next layer. Makeup should be applied last. Happy layering!