When deciding on which products to promote, you can take on a long-term view by looking at the product's Repeat Purchase Rates.
A product that leads to more repeat orders is more valuable than a product that only one-time customers buy. This value means the products are worth optimizing with improvements.
I like to advise focusing on a few product types, in priority-order:
Products with high RPR and a high-ish volume or revenue level. These are solid winners that provide a decent chunk of revenue.
New products with a high RPR. They might not have sold enough to match the volume of long-time ones yet but they could become winners in the middle-term.
Products with a high volume and revenue and a low RPR have the potential for optimization. They are losers in repeat customer-land but since they sell so much, if you can turn them into winners you'd get a high ROI.
All products (and variants for some accounts) are analyzed as part of Repeat Customer Insights' First Product Analysis. You'll be able to spot #1 and #3 products easily, while #2 will require some knowledge about your newest products.
Revisit your optimizations every few months. They shouldn't change dramatically but if you can spot new standout products early on then you can take advantage of them quicker.
Which marketing strategies are producing the best customers for your store?
Analyzing your customers, orders, and products with Repeat Customer Insights can help find which marketing strategies attracted the best customers over the long-term.