These are the five most important KPIs for online retailers:
Conversion Rate - this is the action performed by a user that is desired by the online retailer. This could be, for example, buying a product, subscribing to a product or even creating a user account.  For online retailers, the main goal is to get customers to spend money so the conversion rate would typically be to get users to buy products.
Shopping Cart Abandonment - many sales are lost in the shopping cart right before purchase. This happens when a customer, for example, clicks Buy Now but then doesn’t complete the shopping cart or purchase process. This exit or abandonment can happen for many reasons including if the customer gets turned off by additional fees, a complicated checkout process, or if registration is required before purchase is possible. It’s important to minimize shopping cart abandonment because these customers are so far into the sales funnel that it’s a waste of advertising spend and potential revenue. By fixing the issues as mentioned above and by utilizing advertising retargeting, you can improve your sales funnel and minimize abandonment.
Average Order Value - this is the amount that the average consumer spends during product purchase. By increasing the average order value, an online retailer can become more profitable. You can achieve this increase by bundling products, upselling, encouraging product subscriptions and offering free shipping on orders above a certain value.
Revenue on Advertising Spend - this is the return on investment that you get from online ads by measuring the revenue you earn over the amount that you spend on ads. This helps you determine the effectiveness of your online ads and how you can improve.
Customer Lifetime Value - this is the amount of revenue you stand to earn from a specific customer over his/her lifetime. It is important to help you optimize your marketing expenses and revenue from that customer.