Funnel Framework
Here is a simple framework for identifying high-impact areas in your ecommerce:
From the framework, you're identifying key areas to improve conversion at each step:
Top of the funnel -> You're identifying key development activities and marketing activities that can drive more people into the website. At the same time, and this is something I've seen folks forget, focus also on your post-sales experience. I.E. the entire product delivery and support experience. If your product is good and worthy of people's attention AND you're providing stellar, reliable delivery, the word of mouth would fuel around 20% of your overall traffic.
Middle of the funnel -> Here you're figuring out what merchandizing & development activities can aid in discovery and finalizing of the product(s) that the user wants to purchase. You can do that by interviewing customers and figuring out what their concerns are... main focus areas are speed of discovery (i.e. how quickly can users shortlist products that they like) and speed to decision (i.e. how quickly can they decide from the shortlisted items). There will be technical, merchandizing and UX items here...
Bottom of the funnel -> Here you're figuring out impediments to the final conversion steps. Asking questions like, why do visitors abandon after they've added items to the cart (please ensure you look internally and externally for reasons), why do they leave without making a payment, will lead you to a set of problems that you can then fix. Again, the temptation is to approach it from a technical viewpoint. Think global (as in across the functions - marketing, merchandising, operations, business, buying teams).
Once you have all the necessary items, prioritize them in each of the funnel steps. Remember, it is better to do bottom of the funnel improvements than top of the funnel improvements -> you can always send more people down the funnel, but if the majority are going to drop out, there is no point.