First of all I would learn about the products' features and benefits. I would then understand the customer's needs and recommend complementary or higher-value items. I would use a friendly approach, highlighting the key features of the products, such as better quality, durability, or a limited-time offer, making the customer feel that they are getting added value. For example, if a customer is buying a skincare product, I might suggest a matching beauty tool or an upgraded version with more benefits.