Do you have Google Analytics installed for your Shopify store? If not, then you should do that ASAP.
I’m surprised by just how many Shopify stores don’t have Analytics installed given the amount of insights that you can glean from GA.
If you’re just starting out, you can just have it set up and let it accumulate data while you figure out sales.
Google Analytics Add to Cart Stat
Let’s say that you’re just starting out, you’ve started running Facebook Advertising and you’ve got some add to carts that you see in Shopify and Facebook. But you don’t know for which product.
In this case, you can just go to Conversions -> Ecommerce -> Product Performance
You don’t get this level of detail in the basic Shopify plans and you get to manipulate data in many ways.
Beyond that, you can also look at adding Google Data Studio to make faster decisions with rapid reporting.