Give your customers a chance to purchase additional products that go well together when they're browsing the product pages of your website. If your customer is buying shampoo, give them the possibility to add the conditioner that goes with it in only a single click!
You can display your best sellers to maximize the chances of your products being added to the cart or use algorithms that automatically displays the products that are frequently bought together.
It also increases the internal linking on your website and gives yourself a second chance if one of your users lands on a product that's not what they're looking for or is unavailable.
It also allows you to push the products you want to get rid of to a maximum number of customers and therefore sell them faster. You can also increase that by showing them with a discount.